APPLICATION

How PowerBuilder looks for variables

When PowerBuilder executes a script and finds an unqualified reference to a variable, it searches for the variable in the following order:

1 A local variable

2 A shared variable

3 A global variable

4 An instance variable

As soon as PowerBuilder finds a variable with the specified name, it uses the variable’s value.

1. What events do you know for the application object?

OPEN – the user starts application.

IDLE – no mouse or keyboard activity happens in a specified number of seconds

SystemError – A serious error occurred during execution

CLOSE – the user closes the application

ConnectionBegin –in a distributed computing environment, occurs on the server when a client establishes a connection to the server by calling the ConnectToServer function.

CONNECTIONEND — In a distributed computing environment, occurs on the server when a client disconnects from the server by calling the DisconnectServer function.

2. How can you run another application from within PowerBuilder?

We could do it using PB function Run( ). Run (string {, WindowState}), where string is a string whose value is the filename of the program we want to execute. Optionally, the string can contain one or more parameters of the program; WindowState (optional) is a value of the WindowState enumerated data type indicating the state in which we want to run the program. E.g., Run(“c:\winword.exeleter.doc”, Maximized!)

3. How do you know that the application is already running?

(How do you avoid MessageBox “Application is already running”?)

Use Handle( ) function. Handle( ) returns the object’s name if the object exists.

4. What are the two structures every application has?

Every PowerBuilder application has the MessageObject and the ErrorObject. ErrorObject is used to report errors during execution. MessageObject–to process messages that are not PowerBuilder-defined events, and pass parameters between windows.

5. What are the ways to close your application?

HALT, HALT CLOSE, CLOSE

6.What is HALT? HALT CLOSE? What is the difference between them?

The HALT statement forces the application to terminate immediately. This is most often used to shut down the application after a serious error occurred.

HALT CLOSE Halt Close does the same thing but triggers the application object’s Close event before terminating.

7. What do you do to find out how fast your select is being executed on a client site?

Put TRACE option in the .INI file ( SQL_OPT_TRACE—Connect Option DBParm parameter) Purpose – Turns on/off the ODBC Driver Manager Trace in PB to troubleshoot a connection to an ODBC data source. It provides detailed information about the ODBC API function calls made by PB when connected to an ODBC data source. Values – The values you can specify are:

SQL_OPT_TRACE_OFF (Default) – Turns off the ODBC Driver Manager Trace. SQL_OPT_TRACE_ON – Turns on the ODBC Driver Manager Trace.

8. What are the ways to test correctness of your SQL? SQL Time?

Put TRACE option in the .INI file.

9. What is the purpose of the PB.INI files?

INI stands for “initialization”. They are primarily intended to be a standard format that applications can make use of to hold info from one run to the next. Rather than hard-coding the values of transaction properties in scripts, which is too inflexible for most real-world applications, you’ll want your scripts to read some or all of them from an .INI file. You could use PB.INI

.INIs are always in the same format:

[Database]

DBMS = Sybase

Database = Video Store DB

User Id =

DB Password =

Log Password =

Server Name =

Log Id=

Lock =

DBParm=ConnectString=’DSN=VideoStore DB;UID=dba’

10. How do you manipulate .INI file through PowerBuilder functions?

Set Profile String( )

ProfileString( )

ProfileInt( )

11. How do you set calculator in PB application?

Run (“c:\ calculator” )

SQL

What is SQL?

SQL is A Structure Query Language.

1. Is a standard way of specifying data sets.

2. Is a way to retrieve and manipulate data in DataBase.

3. Is used for all DataBase functions.

4. Can be used in the form of “embedded SQL” from an application program.

1. Which attributes of a Transaction object in PowerBuilder are required to be set for a Sybase/SQLServer connection?

DBMS

Database

UserID

DBPass

Lock

LogID

LogPass

ServerName

AutoCommit

DBParm

2. What is a temporary table?

A temporary table exists only during the current work session.

2a. How do we create temporary tables in Sybase?

We use the pound sign( # ) before the name of the table in the Create Table command, the new table will be temporary. The new table will be created in the Temporary DB, no matter what DB you use when you create it. It exists only during the current work session. If you do not use the pound sign before the table, the table is created as a permanent.

Create table #temppubs

(pub_id pid,

pub_name varchar(30) null)

select title_id, total_orders = sum(qty)

into #qty_table

from salesdetail

group by title_id

3.What is usage of the temporary tables?

Temporary tables are used to hold a set of intermediate results and hold results of queries that are too complex for a single query.

4. What are locks?

Locks are the restriction of data access or modification for specific subset of data in the

DataBase. Locking is handled automatically by SQL Server.

5. Why do we need locks?

We need locks to restrict data access or modification for specific subset of data in the DB.

6. What types of locks in Sybase do you know?

There are Shared (read only) and Exclusive (write only) locks.

Exclusive locks allow only one process to read or write the page. It is used for Update, Insert, Delete. Exclusive locks exist for the duration of a transaction.

Shared locks allow many processes to read, but not one can write. It is used for Select.

Shared locks are normally released as soon as the page has been read.

7. What is a Deadlock?

Deadlock is a condition where two processes, each holding an exclusive lock on the page

that the other processes needs. The process with the lowest accumulated CPU time since login has its transaction rolled back; the other process proceeds to completion.

8. What is an isolation level?

Isolation levels means: higher levels include the restrictions imposed by lower levels.

Defines 4 levels of isolation for SQL transaction:

0 (read uncommitted) allows dirty reads, non-repeatable reads, and phantom rows. (You can see data changed, but not necessarily committed, by another user)

1 (read committed) Prevents dirty reads. Allows non-repeatable reads, and phantom rows.

2 (repeatable read) Prevents (non-repeatable reads) dirty reads and guarantee repeatable reads. Allows phantom rows.

3 (Serializable) prevents phantom reads. Do not allow dirty reads, guarantee repeatable reads and do not allow phantom rows.

The default is 0.

9. What is a DataBase referential integrity?

Referential integrity ensures that data between Primary & Foreign keys is kept consistent.

10. What helps us to support referential integrity?

Triggers help us to support database referential integrity. In relational database system it means that key fields should have correct values across related tables, and also that all changes are propagated to related or associated fields in the database (or distributed DB).

11. What is Primary key? Foreign key?

The primary key of a table is the column or set of columns that are used to uniquely identify each row. If you want to find a specific row in a table, you refer to it with the primary key. Primary keys must be unique and not null. A foreign key reference a primary key in another table.(one or more columns that refer to the primary key of another table) When one table’s column value are presented in another table’s column, the column from the first table refers to the second. OR

A foreign key is a value or combination of values in one table that exist as a primary key in another table. A foreign key defines a relationship between tables. Because a particular table can be related to several different tables, a table may have more than one foreign key. OR

The primary key is one or more columns that uniquely identify a row. The primary key must be unique and not null. (If the primary key has more than one column, it is also known as a composite or compound key.) Foreign key is one or more column that refer to the primary key of another table.

OR

Foreign key is a column (or set of columns) that match the primary key of another table and when the match is found, the data is available for retrieve.

12. What is common key?

Common Key (alternative) One or more columns that are frequently used to join tables.

13. What is an Index?

Index is a pointer which is used to improve performance.

OR

Index is a separate storage structure created for a table to allow direct access to specific data row(s). (Logical pointer to allow faster retrieval of physical data)

14. What is the usage of indexes and how do you create them?

Indexes optimize data retrieval since the data can be found without scanning an entire table. Indexes can also force unique data value in a column.

OR

Indexes are used to improve performance when finding rows, correlating data across tables, ordering results of queries. E.g., to create an index named Cust_ind using the ID column of the Customers table you have to issue the following command in DB Painter:

CREATE INDEX Cust_ind on Customers(ID);

To create unique index:

CREATE INDEX Cust_ind on Customers(ID);

15. What types of indexes do you know in Sybase ?

There are clustered and non-clustered indexes in Sybase. By default indexes are non-clustered, non-unique. We can have only one clustered index and up to 249 non-clustered indexes per table.

Clustered indexes determine the physical order of data in the table

Non-clustered indexes do not affect the data pages and simply provide pointers to rows.

16. When is usage of indexes not effective?

1. The optimiser would prefer the entire table scan if there are < 500 rows in the table.

2. When we have to update our table frequently. We can see if an optimizer chose to use an index by using ‘showplan on’ option. Generally it is up to the optimizer to use indexes or not. It is common opinion that on a small table (<500 rows) the optimiser would prefer a table scan. On a big table (>10 000 rows) usage of indexes is more probable.

17. When does the optimiser ignore the indexes?

When we use like in SQL statement.

18. Do indexes in Sybase affect the physical order of data in the table?

If there is a clustered index on the table, the actual data is sorted in the index order (by the indexed column). Non-clustered indexes do not reorder the actual data (the data is in the order in which it is inserted).

19. If you have a column that gets updated frequently, what kind of index will you create on this column to improve the performance, Clustered or Non-clustered?

Non-clustered. If you create a clustered index on this column, the data will be physically re-arranged in the DataBase after each Update and this will slow down the performance.

20. What do you know about fill factor?

Fill factor of an index specifies how many levels of non-leaf pages the index has.

21. What is the difference between indexes and keys?

Keys are not the same as indexes. Keys are defined at logical design time while indexes are defined at physical design time for performance and other reasons.

22. What is a Transaction?

Transaction is a logical unit of work. We may say it is a set of SQL statements.

23. What is a View? What is the main purpose for a View?

A View is a stored select statement that behaves like a table. The primary purpose of a view is:

Security

Simplify long Query

Ad Hoc Query.

A View is a pseudo-table which contains a select statement from one or more databases.

a. Allows us to combine two databases or two or more tables.

b. For security reasons (it does not let the user obtain real database table.)

c. It is stored as a query in the database.

A View is a virtual table (it is not a real table, it is just an entry in the system catalog). It is a DB object which we use for security purposes or to narrow the scope of data (View does not occupy any space. Only the view created as a result of simple select of all columns from one table can be updated. Cannot use: ORDER BY, COMPUTE, INTO, DISTINCT when creating a rule)

24. What is a Trigger? How do you create a Trigger?

Triggers are a special kind of stored procedures that go into effect when you insert, delete, update data in a specified table or column. Or

Triggers are SQL statements which automatically execute when a row is inserted, deleted, updated in a table. We create a trigger by specifying the table and the data modification commands that should ‘fire’ or activate the trigger. We can create a trigger using the Create clause which creates and names the trigger, the ON clause gives us the name of the table that activates the trigger (called trigger table). The FOR clause tells us that the action for which trigger was created. Example: Create trigger t1

on titles

for insert, update, delete

as

SQL_statement

for (insert, update)

as

if update(column_name)

[(and/or} update(column_name)]. . .

SQL statement

Triggers cannot be called directly. Triggers do not take parameters

25. Which Sybase system tables are used when you write triggers?

The Inserted and Deleted tables are used when writing triggers. Inserted Table holds any rows added to a table when you execute Insert or Update SQL statement. Deleted Table holds any rows removed from

the table when you execute Delete or Update SQL statements.

26. How many triggers can you specify for one DataBase Table?

A table can have a maximum of three triggers : Update trigger,

Insert trigger,

Delete trigger.

However, we can create a single trigger that will apply to all three user actions (Update, Delete, Insert).

27. Which statements are not allowed in a trigger?

In SQL Server’s triggers are not allowed:

Alter Table, Alter Database;

1. Truncate table;

2. Grant and Revoke statements;

3. Update statistics; select into.

5. Creation of objects

6. Neither views nor temporary tables can have triggers.

28. Why do we need Triggers?

To ensure referential integrity. Declarative integrity cannot be used to perform cascaded updates or deletes when the primary key is updated or deleted. The programmer can implement alternative solutions using triggers.

29. How can you obtain the source code of a trigger in SQL Server?

Using sp_helptext <trigger name>

30. Can you call Stored Procedures from Triggers?

Yes.

31. Can you create temporary tables in Triggers?

No, we cannot.

32. What is the difference between HAVING and WHERE keywords in SQL?

WHERE filters out the rows. Where clause limits the rows displayed (eliminates rows, cannot include aggregate functions)

HAVING filters out the groups. HAVING clause limits the groups displayed (eliminates groups, can include aggregate functions, be used with GROUP BY clause). GROUP clause is the command to search through the specified rows and treat all the rows in which the contents of the specified column is identical as one row. As the result, only contents of the specified rows and aggregate functions can be included in the select list for a SQL command using the GROUP BY clause. WHERE clause specifies the connection between tables named in a FROM clause and restricts the rows to be included in the result. HAVING sets conditions for the GROUP BY clause and restricts the groups in the result.

33. Are you familiar with the following terminology:

• Open Client

• ISQL

• Transact-SQL

• APT-WB

• bcp

• DBLib

• OpenServer

• ServerLib

Open Client is a collection of libraries that provides the Application Programming Interface (API) functionality allowing the client to communicate with SQL Server. OR

Sybase Open Client is required in the client application to send request to the SQL Server.

ISQL is a character-based utility that comes with SQL Server. ISQL submits SQL commands to SQL Server and displays the result.

Transact-SQL is used by developers to program organization-wide business rules, queries, transactions and within stored procedures to increase programming efficiency and Database performance.

APT-WB

bcp (bulk copy) is high-speed utility for copying table data to or from an operating system file.

DBLib one of the component of the open client

Open Server is a server that you write. (developer’s tool kit which enables any data source or service to become a multi-threated server

ServerLib

34. What is Data Dictionary? How is it used?

Data Dictionary is stored in each database. The info regarding the database(s) structure and components is contained in the data dictionary for the database. The data dictionary, also called the “system catalog”, is stored as data in the “system tables” in each database.

35. What is the name of the DataBase in which system-related information is stored?

Master Database which has system catalog, system procedure . .

36. What are the system databases in SQL server?

Beside user’s databases SQL SERVER always has 3 databases: MASTER, MODEL, and TempDB. Stored procedure DB

MASTER is used internally by SQL Server to store information about user’s databases;

MODEL is used as a template to create a new user’s database.

TempDB is used to store temporary info like temporary tables if you use them in SPs.

37. How do you create a DataBase? What parameters can you specify while doing Create?

We have to use Create Database statement and define Database name, devices for our database and size in Mbytes.

38. How do you display information about the DataBase?

sp_helpdb

39. How can you switch to another database?

Connect using db_name

40. What is a Rule? What are the steps for creating and using a Rule?

A Rule is a DataBase object that defines a restriction on a column. A Rule can specify an edit mask for a column or user-defined datatype. A Rule can be a list of values, a range of values or an edit picture. 1. Create a rule with the CREATE RULE command

create rule age_rule as

@age < 110

2. Bind a rule to a column with sp_bindrule

sp_bindrule ‘age_rule’, ‘my_table_age’

sp_bindrule ‘pub_rule’, ‘publishers.pub_id’

3. Unbind a rule from an object with sp_unbindrule

sp_unbindrule ‘authors.zip”

4. Drop a rule using drop rule rulename.

We cannot drop a rule if it is bound to a column. Unbind it first.

The last rule bound to a datatype/the column is the only one that takes effect on the datatype/the column. The rule bound to a column overrides the rule bound to the column’s datatype.

Rules are a specification that controls what data can be entered in a particular column.

1.Create a rule : create rule age_rule as @age<8

2.Bind a rule to a column : sp_bindrule ‘age_rule’,’mytable.age’

3.Unbind a rule from an object :sp_unbindrule ’mytable.age’

4.Drop a rule : drop rule age_rule

5. Examining rules using the Data Dictionary.(in SQL you can sp_helptext

sp_helptext pub_idrule( writes all information about our rules)

41. What is a Default? How do you use it?

A Default is a value that is applied on an insert if no value is supplied.

Defaults specify the data to be entered into a column if user does not specify it on input.

Or

Default is the data to be entered in a column if none is provided by user.

42. How can you remove a column from a table?

We cannot. We can either drop or recreate the table without the column, or copy selected columns of your table into a new table with a different definition.

43. What does the following SQL do:

SELECT title FROM titles

WHERE title like ‘%[Ss]ecret%’

44. What does the following SQL do:

SELECT distinct type, price, title FROM titles

WHERE price > (SELECT avg(price) FROM titles)

45. What are the inserted and deleted tables?

The deleted table stores copies of the affected rows during delete and update statements.

The inserted table stores copies of the affected rows during insert and update statements.

These are temporary tables used in trigger tests. Use these tables to test the effect of some data modification and set conditions for trigger actions. You can’t directly alter the data in the trigger test tables but you can use these tables in Select statement to detect the effects of an insert, update, delete.

46. What is the SA? DBO? What are their purposes?

SA—system administrator—(super-user with a broad range of privileges. Can assume the identity, and thus the privileges, of any other user). The user with SA role allocates resources and maintains the data server.

DBO—DataBase Owner—a special user within a database having certain database-wide capabilities.

47. Write an SQL to find an average price for all titles published between 1975-1980.

SELECT avg( price )

FROM titles

WHERE publishers .date > 1975 AND publishers .date < 1980 or using between keyword.

48. What is the purpose of IF EXITS clause?

IF EXIST stops processing a query once it finds the first match.

Is there an author with the last name ‘Smith’?

Declare @lname varchar (40)

select @lname = “Smith”

IF EXIST (select * from authors

where au_lname = @lname)

select “There is a” + @lname

ELSE

select “There is no author called” + @lname

49. What is a Cursor?

A Cursor is a symbolic name that is associated with a Transact-SQL statement. A Cursor provides the ability to step through the result set row by row. The application program can perform processing on each row.

50. What is the purpose of CURSOR? How and when can you declare a CURSOR?

The purpose of Cursor is to allow a program to take action on each row of a query result set rather than on the entire set of rows returned by select statement. A Cursor must be declared before it is used. The syntax to declare a Cursor can be included in a stored procedure or an application. Provides the ability to delete or update a row in a table based on the cursor position. Acts as a bridge between the set orientation of an RDBMS and row-oriented programming.

51. What is the syntax to use a Cursor?

To use a Cursor :

Declare the cursor for the select operation you are performing

Open the cursor

Fetch each row in the cursor for processing, repeating until all rows are processed

Close the cursor

Deallocate the cursor

52. What is an outer join? What kind of outer joins do you know?

An outer join is defined as a join in which both matching and unmatching rows are returned. We use *= to show all the rows from the first defined table. (Left outer-join)

We know left outer join and right outer join.

53. How do we join two or more tables?

We use Select statement with Where clause, where we specify the condition of join.

54. Give an example of outer join?

An outer join forces a row from one of the participating tables to appear the result set if there is no mattering row. An asterisk(*) is added to the join column of the table which might not have rows to satisfy the join condition. For example:

SELECT cust.cust_id, cust.cust_lname, sal.sal_id

FROM customer cust, salesman sal

WHERE cust.sal_id *= sal.sal_id

Used for reports. There is no matching between two columns.

55. How do you understand left join?

56. How do you get a count of returned rows?

Using a global variable @@rowcount.

57. How do you get a Count of non null values in a column?

Count (column_name) returns number of non null values in the column.

57. What are the aggregate functions? Name some.

Aggregate functions are functions that work on groups of information and return summary value.

Count(*) number of selected rows;

count(name_column) number of non-null values in a column;

max( ) highest value in a column;

sum( ) total of values in a column;

min( ) lowest value in a column

avg( ) average of values in a column.

Aggregates ignore Null value (except count(*)).

Sum() and avg() work with numeric values.

Only one row is returned (if a GROUP BY is not used).

Aggregates may not be used in WHERE clause unless it is contained in subquery:

(select title_id, price

from titles

where price >(select avg(price) from titles).

58. What can be used with aggregate functions?

1. More than one aggregate function can be used in a SELECT clause.

SELECT min(advance), max(advance)

2. DISTINCT eliminates duplicate value before applying aggregate. Optional with sum(), avg() and count. Not allowed with min(), max() and count(*)

SELECT avg(distinct price)

59. What is a Row?

A Row contains data relating to one instance of the table’s subject. All rows of a table have the same set of columns.

60. What is a Column?

A Column contains data of a single data type (integer, character, string), contains data about one aspect of the table’s subject.

61. Where do you use GROUP BY?

GROUP BY organizes data into groups.

1. Typically used with an aggregate function in the SELECT list. The aggregate will then be calculated for each group.

2. All Null values in the group by column are treated as one group

SELECT type, price = avg(price)

FROM titles

GROUP BY type;

3. With a WHERE clause – WHERE clause eliminates rows before they go into groups. Will not accept an aggregate function

SELECT title_id, sum(qty)

FROM salesdetail

WHERE discount > 5

GROUP BY title_id

4. With HAVING – HAVING clause restricts group. Applies a condition to the group after they have been formed. HAVING is usually used with aggregates.

SELECT avg(price), type

FROM titles

GROUP BY type

HAVING avg(price) > 12.00

62. What is a subquery or a nested select?

A Subquery is a select statement used as an expression in a part of another select, update, insert or delete statement. Subquery is used as an alternative method to Join clause and provides additional functionality to the Join clause

SELECT title

FROM titles

WHERE pub_id = (SELECT pub_id

FROM publishers

WHERE pub_name = “New Age Book”)

63. Why do you use a Subquery instead of a join?

Because they are sometimes easier to understand than a join which accomplishes the same purpose. To perform some tasks that would otherwise be impossible using a Join clause (using an aggregate).

64. What are restrictions on a Subquery?

Subqueries cannot be used with : 1. Keyword INTO:

2. With ORDER BY

3. With computed clauses.

The DISTINCT keyword cannot be used with Subqueries that include a GROUP BY clause.

65. What is Simple Retrieval?

Used to retrieve data from DataBase.

66. What operators in SQL do you know?

= equal

> greater than

< less than

>= greater than or equal to

<= less than or equal to

!= not equal

<> not equal

!> not greater than

!< not less than

Logical operators

67. What is Re-ordering Columns?

The order of column names in the SELECT statement determines the order of the column in the RESULT.

SELECT state, pub_name

FROM pub

RESULT

state pub_name

68. How do you eliminate Duplicates?

DISTINCT eliminates duplicate in the output.

69. How do you Rename Columns?

Use new_column_name = column_name

SELECT ssn = user_id, last_name = lname.

Use a space to separate column_name and new_column_name

SELECT user_id ssn, lname last_name

70. What is Aliases?

To save typing the table name repeatedly, it can be aliased within the query.

SELECT pub_name, title_id

FROM titles t, publishers p

WHERE t.pub_id = p.pub_id and price = 19.9

71. Can you join more than two tables?

Yes. The Where clause must list enough Join conditions to connect all the tables.

72. Can you use Joins with ORDER BY and GROUP BY?

Yes, we can. SELECT title. title_id, qty, price * qty, price

FROM titles, salesdetail

WHERE title.title_id = salesdetail.title_id

ORDER BY price * qty;

SELECT stor_name, salesdetail.stor_id, sum(qty)

FROM salesdetail.stor_id = stores.stor_id

WHERE salesdetail.stor_id = stores.stor_id

GROUP BY stor_name, salesdetail.stor_id;

73. Can you use Joins with additional conditions?

Yes, we can SELECT s.stor_id, qty, title_id, store_name

FROM salesdetail sd, stores s

WHERE sd.stor_id = s.stor_id and qty > 35

74. What is Character String in Query result?

Adding character string to the SELECT clause

SELECT “The store name is”, stor_name

FROM

Result stor_name

The store name is PowerBuilder

75. What does ORDER BY do?

The ORDER BY clause sorts the query results(in ascending order by default)

1. Items named in an ORDER BY clause need no appear in the select-list.

2. When using ORDER BY, Nulls are listed first.

76. What is a Cartesian Product?

Cartesian Product is a set of all possible rows resulting from a join of more than one table. If you do not specify how to join rows from different tables, the system will assume you want to join every row in each table. Cartesian Product is concatenation of every row in one table with every row in another table. This way if first table has n rows and second has m rows, so the product table will have n*m rows.

77. Give an example of Cartesian product.

Cartesian Product is the set of all possible rows resulting from a join of more than one table. For example: SELECT customer_name, order_No

FROM customers, orders

If customer had 100 rows and orders had 500 rows, the Cartesian product would be every possible combination – 5000 rows. The correct way to get each customer and order listed (a set of 500 rows) is: SELECT customer_name, order_No

FROM customers, orders

WHERE customer.cust_No = orders.cust_No

78. What are the SQL differences?

Differences in object naming, facilities available on a server, implementation, syntax, data definition language, commenting, and system table technique differences. When we are trying to build an application using data from multiple sources, we should be aware of it.

79. If you ensure referential integrity in Sybase DataBase with both foreign keys and triggers, which one will be fired (checked) first?

Foreign key.

80. How can you convert data from one data type to another using Transact-SQL in Sybase?

There is a function Convert( ) in Transact SQL which is used for data conversion.

For example, to convert DataTime column into string you could write something like

SELECT CONVERT(char(8),birthdate,1)

in this case third parameter specifies format of returned string(“mm/dd/yy”)

81. What is a Union?

The Union operator is used to combine the result sets of two or more Select statements. The source of data could be different, but each Select statement in the Union must return the same number of columns having the same data type. If we use Union, all it will return all rows including duplicates. UNION operator combines the results of two or more queries into a single result set consisting of all the rows belonging to A or B or both. Union sorts and eliminates duplicated rows.

82. From Employee table how to choose employees with the same Last Name, First Name can be different?

Use SelfJoin. (look at the table as at two different)

SELECT a.first_name, b.last_name

FROM a.student,b.student

WHERE a.student.student_id = b.student.student_id

83. How can you handle Nulls values in DataBase?

We have to make sure that columns that are part of the primary key( or just an important column) are not nulls in table definition.

If IsNull (column)

if not IsNull(column)

84. How can you generate unique numbers in DataBase?

DataBase has special system column that keeps all used unique numbers. Special system function reads last used number and return next to use.

85. What’s the minimal data item that can be locked in a DataBase?

Data page.

86. How many types of Dynamic SQL do you know in PowerBuilder?

There are 4 types of Dynamic SQL in PowerBuilder:

Format 1 Non-result set statements with no input parameters

Format 2 Non-result set statement with input parameters

Format 3 Result set statements in which the input parameters and result-set columns are known at compile time

Format 4 Result set statements in which the input parameters, the result-set columns, or both, are unknown at compile time

87. When and why do we need Dynamic SQL?

To perform some execution of the SQL statements at runtime.

88. We have table T and columns C1 and C2. Prepare Select statement which would have all possible combinations of values from C1 and C2.

SelfJoin

91. Find employees who work in the same state with their managers? (2 tables, 1 – for employee, the other for managers’ info. 1st may have only manager but they can work in different states, 1 manager has many employees in different states)

Use outer join

COMMON TECHNICAL QUESTIONS

1. Deleting a row that is a foreign key in another table violates what kind of DB rule? Referential integrity

2. Why would you code a commit?

To complete a unit of work

3. What is a Database transaction?

Logical unit of work

4. What is the language for creating and manipulating Database?

• DML

• DDL

• DLL

5. User defined function for a window can only be called if the window is active?

6. In the script painter for an inherited window, you can either Extended or ———— the ancestor script?

7. What is the method to validate a numeric column in a DW?

8. When a ORDER_NUM is selected by user, how do you highlight the details of the specific ORDER?

9. What does the “pass by value” in the function definition mean?

9. The database-specific error codes for connect/update/retrieve are stored in what attribute of the transaction object?

11. Why would you use THIS or ParentWindow? (pick all correct answers)

-polymorphism

-inheritance

-instance

12. Which are valid for a menu?

-ParentWindow.Title = “Title”

-Close(ParentWindow)

-ParentWindow.st_title = “title”

13. What do a Pop-up and Response windows have in common?

-they both open on top

14. What type of a window is modal?

-response

15. What is a class?

-definition of an object

-instance of an object

Data Pipeline

1. What is the Data Pipeline?

The Data Pipeline lets us copy tables and their data from one Database to another even if the Databases are on different DBMS. We can also use the Data Pipeline to copy data within the same database (several tables into a single table).

2. What is the data sources for a data pipeline?

Quick Select

SQL Select

Query

Stored Procedure

3. What can you do with the Data Pipeline ?

We can use the Data Pipeline to:

Create (add) a table in the destination (target) database

Replace (drop/add) an existing table in the destination database

Refresh (delete/insert) rows in the destination database

Insert rows in the destination database

Update rows in the destination database

4. What happens if an error occurs when piping data ?

When errors occurs in a Data Pipeline, an Error Message window appears. It shows:

the name of the table in the destination database where the error occurred

the option that was selected in the Data Pipeline dialog box

each error message

the values in the row in which each error occurred.

5. How do you create a Pipeline as a part of an application?

Including data pipeline in an application involves Window Painter, Data Pipeline Painter, User Object Painter and scripts. A number of objects are involved in setting up a pipeline in an application:

• two transaction objects

• pipeline object

• standard class pipeline user object

• DataWindow control (to display row errors).

6. In what event can you access the current number of row errors ?

In PipeMeter event using RowsInError attribute.

A pipeline has the following events:

• PipeStart, when a Pipeline or Pipe Repair operation starts

• PipeMeter, when a block of rows has been read or written

• PipeEnd, when a Pipeline or Pipe Repair operation ends

Attributes:

• RowsRead

• RowsWritten

• RowsInError

1. What is a DataStore?

A DataStore is a nonvisual DataWindow control.

A DataStore acts just like a DataWindow control except that many of the visual properties associated with DataWindow controls do not apply to a DataStore. However, because you can print a DataStore, PowerBuilder provides some events and functions for a DataStore that pertain to the visual presentation of the data.

2. When do you use a DataStore?

If I have some data which need to be displayed in more than one window of my application, I would use a DataStore instead of the Retrieve( ) function.

DATABASE PAINTER

1. What is the Relational DataBase model?

Data in a relational DB is stored in tables; tables are composed of rows and columns; each row describes 1 occurrence of entity; each column describes 1 characteristic of an entity.

2. What is the DataBase?

DataBase is a body of data in which there are relationships among the data elements.

3. What is DataBase Management System?

DBMS is Software that facilitates the function of DataBase structures and the storage and retrieval of data from those structures.

4. What are extended table and column attributes? Why are they useful?

Extended table and column attributes are defaults that provide a standard appearance to the data and headings in DW objects. We don’t have to specify the characteristics every time we create a DW object from columns in the table. Extended column attributes create and maintain the display and validation formats, edit masks, and initial values for columns as they appear in PB applications. They are stored in the DB in system tables that are created by PB. Once we define them, we can apply them to as many columns as we need. Extended table definition are data in a table, column headings, labels for columns.

Extended column attributes are :

1. Format -select the default display format for the data in the column

2. Edit – selects the default edit mask for the data in the column

Validation Select the default validation rule for the data in the column

Header – enters the heading to be used for the column in all reports/data window

comment – enters comments to further the columns content. Any comments entered for the column automatically generates a tag value for that column

Justify selects the justification for the column(left, right, centred)

Height – enters a default height for the column

Width – enters a default width for the column

Initial – enters an initial value for this column to be set to for new records

10. label enters the label to be used for the column in all reports/data windows

The extended table and column attributes are defaults that are useful in application development because:

1. They provide a standard appearance to the data and heading in DataWindow object.

2. Relieve the burden of specifying the characteristics every time you create a DW object from columns in the table

5. What is a Table?

A Table is Relational Model. In a relational DataBase, all data is in tables. A table holds data relating to particular class of objects (an entity).

6. What are validation rules? Why are they useful?

Validation rules are expressions that PowerBuilder uses to validate user-entered data. Validation rules are automatically checked by the DataWindow object when data are entered in the column. DBMS has no knowledge of it.

7.What is the difference between an edit style and a display format?

Do these attributes depend on the Database being used?

FORMAT is used to display data in the column.

EDIT is used to enter data in the column

No. They do not depend on Database being used.

8. For what purpose can you use the Data Manipulation tool?

The Data Manipulation tool within the database painter provides an easy to use interface to allow you to add, update and delete data from tables on the database.

9. For what purpose can you use the Database Administration tool?

The Database Administration tool within the DB painter provides a workspace for you to control access to the DB and the DB tables, paint or enter SQL statements or execute any SQL statement that you have created.

10. What is the purpose of a transaction object?

11. While in Database Painter, you can alter the extended attributes for the table.

12. When do you need to perform Synchronise PowerBuilder attributes (menu Options (Design) in the DataBase Painter)?

If you drop a table or column outside of PB, orphaned info remains in the PB tables that contains extended table/column definition info (PBCATTBL, PBCATCOL, PBCATFMT, PBCATVLD, PBCATEDT). So you use this option to delete this orphaned info.

59. What types of Database constrains do you know?

user-defined data type;

default;

rule;

primary – foreign key.

2. What are validation rules? What are they useful for?

Validation rules are expressions that PowerBuilder uses to validate user-entered data. Validation rules are automatically checked by the DataWindow object when data are entered in the column. DBMS has no knowledge of it.

3. What is the difference between an edit style and a display format?

Edit style is format of a column during user input.

Display format is format of the data when it is displayed.

4. What is the Data Manipulation tool?

For what purposes can you use the Data Manipulation tool?

Data Manipulation tools allow us to display data, add or delete rows and change existing values. They provide an easy-to-use interface to allow us to add, update, and delete data from tables in the Database and perform various Database administration functions.

5. What is the Database Administration tool?

For what purposes can you use the Database Administration tool?

The Database Administration tool allows you to code and execute SQL commands that you have created.

6. Could you describe what a database consists of?

A Database consists of Tables, Indexes, Datatypes, Defaults, Rules, Triggers and Stored Procedures.

A Table is a data repository structured as a grid with columns and rows. The columns are the data items (or fields). The rows are iterations of that data in the form of records. (Also, a collection of records referred to as rows that associates fields that are referred to as columns.)

Indexes are a set of pointers that are logically ordered by the value of a key and are used to provide quick access to the data.

Datatypes specify what type of information each column will hold and how the data will be stored.

Defaults default data to be entered in a column if none is provided by the user.

Rules are a specification that controls what data can be entered in a particular column.

Triggers are special kinds of SPs that go into effect when you insert, delete or update data in a specific table. Triggers are used to maintain the referential integrity of your data by enforcing the consistency among logically related data in different tables.

Stored Procedures is a collection of SQL statements and control-of-flow language.

7. How do you create a database?

We have to use Create Database statement and define Database name, devices (rules) for our Database and size in Mbytes.

8. How do you obtain information about a specific Database?

Using System Stored procedure SP_Helpdb

9. How can we modify the existing tables?

We can add one or more columns (always allow NULL) but we cannot remove columns from the table. The table must be dropped and recreated.

10. What Microsoft server tools do you use when working with Databases?

SQL Administrator—to connect to the Database to manage devices, log in databases.

Object Manager—to manage tables, indexes, triggers, stored procedures and rules.

Microsoft ISQL—to write and run SQL statements.

11. What do you use triggers for?

Triggers are used for referential integrity processing to maintain relationship between primary and foreign keys.

12. How do you maintain referential integrity between primary and foreign keys?

If we delete rows from the table with primary keys, we have to do something with tables where these PRIMARY KEYS ARE FOREIGN KEYS. We can delete rows with a foreign key or set them to NULL or give a message to the user and let them decide. If we change or create Foreign keys, we have to validate them against their associated Primary key.

13. Do we have to execute the Trigger?

No, if the triggers are defined for a specific table for a specific process (insert, delete, update) and if we have a trigger for, say, the delete process for a specific table DELETE trigger will be executed automatically.

14. If there is a problem with the DATABASE during data retrieval, which DW event will be triggered? Where will the error code be stored?

DB Error Event

DB Error Code

Connecting to a Database

15. What is a transaction?

A transaction is a sequence of one or more SQL statements that together form a logical unit of work. A transaction is a sequence of operations or events in the DB. The beginning of a Transaction is the first SQL statement in the logical unit of work; the end of the Transaction is marked by a Commit or Rollback or their equivalents. The SQL statements we use to make and break Database connections and manage database transactions are:

Connect—establishes the connection to the database

Commit—applies all changes made to the Database since the last point of Database integrity Commit executes all changes to the database since the start of transaction (or since the last Commit or Rollback) become permanent.

Rollback—rolls out all changes made to the DB since the last point of DB integrity

Disconnect—breaks the connection to the Database.

Rollback executes all changes since the start of the current transaction are undone.

16. What transactions do you know?

Commit, Rollback, Connect, Disconnect

17. Why is the concept of transaction important?

We need to manage Database connections and transactions through the use of embedded SQL statements Connect, Commit, Rollback, and Disconnect, especially for transactions involving updates to the Database.

18. What is a PB Transaction object?

PB transaction object is a communication area between PC and the database. For each database that we use in our project there has to be a separate transaction object.

The Transaction object specifies the parameters that PB uses to connect to a DB.)

19. What is a Transaction Object?

A Transaction object is a global nonvisual PowerBuider object used to store connection information for a particular server and provide error checking. It is a structure used to specify DB info and provide error checking. (Info in the object is used for the initial connection, and the messages from the server are returned to the application through the object. This object is fundamental to maintaining connections to multiple data sources.

20. What do you have to do to connect to the database in your project?

We have to assign values to the attributes of our transaction object such as DBMS, Server name. . . We usually keep these values in the application .INI file, and in the Open event for our Application object we use ProfileString() function to get these values and assign them to the attributes of the transaction object.

21. What is a logical unit of work?

It is a transaction.

22. What statement inside PB deals with a transaction?

Connect starts the transaction (establishes connection to DB)

Disconnect terminates a transaction.

Commit executes all changes to the DB since the start of transaction (or since the last Commit or Rollback) become permanent.

Rollback cancels all database operations in the specified database since the last COMMIT, ROLLBACK, or CONNECT

23. What is SQLCA?

It is a default transaction object that PB provides for us to communicate with one Database. We don’t have to create this transaction object and destroy it.

24. What is SQLCode?

SQLCode is an attribute of the transaction object that we check after any SQL statement to find out if the transaction was successful or failed.

25. To use multiple databases in your application, what do you do?

We use the default Transaction object for one and for the others we have to create the

Transaction object with CREATE transaction statement and at the end DISCONNECT to destroy this transaction with DESTROY statement.

26. How do we handle errors in the script?

We test the success or failure of any SQL statement, checking SQLCode attribute. If it fails (-1), we give the message using MessageBox() and display SQLErrorText attribute.

27. What is the purpose of a transaction object ?

The purpose of a transaction object is to identify a specific Database connection within a PowerBuilder application.

28. How can you do Transaction Management in PowerBuilder?

We can do it using the AutoCommit attribute of the Transaction object. If the value of AutoCommit is TRUE, PowerBuilder just passes our SQL statements directly to server and each statement is then automatically committed to the Database as soon as it is executed. If we set the value of AutoCommit to FALSE (default value), PowerBuilder requires that we use the Commit and RollBack key words to commit and rollback our transaction when we are finished with it. In this case PowerBuilder begins the new transaction automatically as soon as we Connect, Commit or RollBack, Disconnect.

29. How can you provide Transaction Management in PowerBuilder?

By using statements CONNECT; DISCONNECT; COMMIT; ROLLBACK. We can improve performance by limiting the number of Connects and Disconnects.

30. The attributes of a transaction object can be divided into two groups.

Describe the purpose of those two groups.

Some attributes are used to make the connection to the database. They are:

• DBMS

• Database

• UserID

• DBPass

• Lock

• LogID

• LogPass

• ServerName

• AutoCommit

• DBParm

Some attributes return status info to the application, returned by DBMS. They are :

SQLDBCode

SQLErrText

• SQLReturnData

• SQLCode

• SQLNRows

31. Under what circumstances is it necessary to define and instantiate a

transaction object in addition to SQLCA?

If our application needs to access more than one Database, we will need to define and

instantiate (create) additional transaction objects.

32. List the steps required to establish a connection between a PowerBuilder

application and a Database.

The sequence of coding tasks to connect to a Database is

• Define (declare) and instantiate (create) a Transaction object;

• Assign values to the attributes of the Transaction object

• Do CONNECT;

• Check the success or failure of the Database connection.

33. What must you code at the end of every embedded SQL statement?

All embedded SQL statements must end with a semicolon (;).

34. What is embedded SQL ?

Embedded SQL refers to the use of SQL statements in our PowerScript code. All embedded SQL statements begin with an SQL verb and end with a semicolon (;).

When we need a reference to PowerBuilder variables in embedded SQL statements, we put a colon (🙂 before the PB variable.

35. What syntax do we use to connect with our own transaction object?

If we are using a Transaction object we have defined, we must use the full statement:

CONNECT using trans_name;

36. How can you define an additional Transaction object? When might you need it?

To create an additional transaction object, we first declare a variable of type transaction, then we create the object and then define the attributes that will be used. Declare a variable of a transaction object type and then specify parameters to connect to the database.

Define (declare) — Transaction To_Sybase

Instantiate a Transaction object; To_Sybase = Create transaction

Assign values to the attributes of the Transaction object

To_Sybase.DBMS = “Sybase”

To_Sybase.DataBase = “Personnel”

To_Sybase.LogId = “DD25”

Do CONNECT;

connect using To_Sybase;

Check the success or failure of the Database connection.

If SQLCA.SQLCode <>0 then

MessageBox (“Warning”, “SQLErrCode”)

We create an additional Transaction object if we need to access data in our application from more than one DataBase. You can create an instance of the standard Transaction object. You have to populate it and destroy after using. You might need it when you want to connect to several DB at the same time.

37. Name some attributes of a transaction object.

DATABASE (String)—The name of the database with which you are connecting.

DBMS (String)—PowerBuilder vendor identifier.

DBParm (String)—DBMS-specific parameters.

DBPass (String)—The password that will be used to connect to the database.

Lock (String)—The isolation level.

LogID (String)—The name or ID of the user who will log on to the server.

UserID (String)—The name or ID of the user who will connect to the database.

LogPass (String)—The password that will be used to log on to the server.

Server Name (String)—The name of the server on which the database resides.

SQLCode (Long)—The success or failure code of the most recent operation.

Return codes: 0—Success; 100—Not Found; -1—Error (use SQLDBCode or SQLErrText to obtain the details)

SQLDBCode (Long)—The database vendor’s error code.

SQLErrText (String)—The database vendor’s error message.

SQLNRows (Long)—The number of rows affected (the DB vendor supplies this number, so the meaning may not be the same in every DBMS).

SQLReturnData (String)—DBMS-specific information.

AutoCommit (Boolean)—The automatic commit indicator (SQL Server only).

Values are: True — Commit automatically after every database activity

False — Do not commit automatically after every database activity.

38. The end user cannot connect to the Database w/o a PB.INI?

true

39. In Client/Server the Database engine must be on a dedicated server

false

DATAWINDOW OBJECT

1. Describe the two major aspects or components of a DataWindow object.

Data Source is a way to populate a DataWindow object with data.

Presentational style provides a default format for the data. The styles include Tabular, Grid, FreeForm, Labels, N-up, Groups, Graphs and Crosstabs. We can use any of the presentation styles with any of the data sources. PowerBuilder also provides extensive facilities such as rearranging data items, sorting them, or adding graphical elements such as lines, circles or boxes.

2. DataWindow objects most often obtain their data from relational Databases.

Name three other sources of their data.

• User Input

• .TXT or .DBF files

• DDE with another Windows application

3. Which Data Source in the DataWindow painter is itself an object?

• Query

4. What Data Sources do you know and how do you use them?

The Data Source determines how we select the data that will be used in the DW object.

If the data for the DataWindow object is retrieved from a database, we may choose one of the following Data Sources:

Quick Select is a select from one or multiple tables that are joined through foreign keys and may include simple selection criteria which appear on the WHERE clause. We can only choose columns, selection criteria, and sorting. We cannot specify grouping before rows retrieved, include computed columns, or specify retrieval arguments.

SQL Select is an SQL Select statement from one or more tables in a relational database

and may include selection criteria that appear on any of the possible Select statement clauses (can include selection criteria (WHERE clause), sorting criteria (ORDER BY clause), grouping criteria (GROUP BY and HAVING clauses), computed columns, one or more arguments to be supplied during execution.

Query is a predefined SQL Select statement, which must be previously constructed and saved as a Query object.

Stored Procedure indicates that the DataWindow will execute a Stored Procedure and display the data in the first result set. This Data Source only appears if the DBMS to which PowerBuilder is connected and which supports Stored Procedures. We can specify that the data for a DataWindow object is retrieved through a stored procedure if our DBMS supports Stored Procedures.

External is used when the data is not in the database and the DataWindow object will be populated from a script or data will be imported from a DDE application. If the data is not in the DB, we select External as the Data Source. This includes the following situations:

• If the DataWindow object is populated from a script

• If data is imported from a DDE application

• If data is imported from an external file, such as a tab-separated text file (.TXT file) or a dBASE file (.DBF file).

External indicates that we have coded a script that supplies the DataWindow object with

its data. We use this Data Source when the data is in a .TXT or .DBF file or obtained through DDE. We may also use it when we plan to obtain the data by embedding our own SQL Select statement in a script. With this Data Source the DataWindow object does not issue its own SQL statement. We specify the data columns and their types so that PB can build an appropriate DataWindow object to hold the data. These columns make up the result set. In a script, we will need to tell PowerBuilder how to get data into the DataWindow in our application. Typically, we will import data during execution using a PowerScript Import function (such as ImportFile() and ImportString() or do some data manipulation and use the SetItem( ) function to populate the DataWindow.

5. Under what circumstances will PowerBuilder automatically join tables that

you select in the Select painter?

If we select tables that have one or more columns with identical names, the Select painter

automatically displays the join, assuming equality between the two columns.

6. What Presentation Styles do you know and when do you use them?

The Tabular presentation style presents data with the data columns going across the page and headers above each column. As many rows from the database will display at one time as can fit in the DataWindow object. We can reorganize the Tabular presentation style any way we want by moving columns and text. Tabular style is often used when we want to group data.

The Freeform style presents data with the data columns going down the page and labels next to each column. We can reorganize the default layout any way we want by moving columns and text. Freeform style is often used for data entry form.

The Grid style presents data in a row-and-column format with grid lines separating rows and columns. Everything we place in a grid DataWindow object must fit in one cell in the grid. We cannot move columns and headings around as we can in the Tabular and Freeform styles. But, unlike the others styles, users can reorder and resize columns with the mouse in a grid DataWindow object during execution.

The Label style presents data as labels. We choose this style to create mailing labels or other kinds of labels. If we choose the Label style, we are asked to specify the attributes for the label in the Specify Label Specification.

The N-Up style presents two or more rows of data next to each other. It is similar to the Label style. We can have information from several rows in the database across the page, but the information is not printed on labels. The N-Up presentational style is useful if we have periodic data; we can set it up so each period repeats in a row.

We are asked how many rows to display across the page. For each column PowerBuilder defines n columns in the DataWindow (column_1 to column_n), where n is the number we specified in the preceding dialog box.

The Group presentation style provides an easy way to create grouped DW objects, where rows are divided into groups, each of which can have statistics calculated for it. It generates a tabular DW that has one group level and some other grouping properties defined. We can customise the DataWindow in the DataWindow painter workspace.

The Composite presentation style allows us to combine multiple DWs in the same object. It is handy if we want to print more than one DataWindow on a page.

The Graph presentation style creates a DataWindow object that is only a graph – the underlying data is not displayed. As the data changes, the graph is automatically updated to reflect the new values. We use a graph to enhance the display of information in the DataWindow object such as a tabular or freeform DataWindow.

Crosstab processes all the data and presents the summary information that we have defined for it. We use if we want to analyse data. Crosstab analyses data in a spreadsheet. Instead of seeing a long series of rows and columns, users can look at a Crosstab that summarises the data.

OLE 2.0 presentation style using a process called uniform data transfer; info from PB supported data sources can be sent to an OLE 2.0 server application. The OLE 2-compliant application uses the PB supplied data to formulate a graph, map, a spreadsheet or the like to be displayed in the DW.

RichText presentation style using a RichText DW, you can create letters of other documents by merging info in your DB into a formatted DW. Master word processing oriented features such as headers, footers and multiple fonts are available in an easy-to-use format.

7. Describe the difference between the grid and tabular presentation styles.

In the Grid presentation style, we cannot move columns and headings around as we can in the Tabular presentation style but in Grid presentation style users can reorder and resize columns with the mouse during execution.

8. Describe the difference between the labels and N-up presentation styles.

In N-up style, we can also have information from several rows in the database across the page, but the information is not printed on labels.

9. How often must you set the Transaction object ?

Just once when we define the DW control. If we change the association of a DataWindow object with a DataWindow control in a script, we must re-issue the SetTransObject () before the next retrieval or update.

10. What function changes the current row?

ScrollToRow( )

11. If you need to highlight a row and bring it into view, which function would you

issue first: SelectRow() or ScrollToRow()? Why ?

1. SelectRow( )

2. ScrollToRow( )

Because the row may already be displayed.

12. Name the three DataWindow buffers.

There are officially 3 buffers:

Primary–contains all data that have been modified but has not been deleted or filtered out.

Filter – data that was filtered out.

Delete – contains all deleted data from the DataWindow object.

Therefore we know 4^th– Original that keeps original data from Database.

13. When do the four levels of validation for DataWindow occur?

As a user tabs from one item to the next, PowerBuilder performs four levels of validation

• when user modifies column

• when user tabs or clicks elsewhere in the DataWindow

• when item loses focus

14.Which two events may be involved in the four levels of validation ?

An ItemChanged Event occurs when an item in a DataWindow has been modified and loses focus.

An ItemError Event occurs when a user has entered or modified data in an item in a DataWindow control and one of the following occurs:

– the data type of the input does not match the data type of the column (#2)

– the input does not meet the validation criteria defined for the column (#3)

– the input does not satisfy the processing in the script for the ItemChanged event (#4)

15. How would you define validation rules for the Datawindow object?

We can define validation rules in the DataWindow painter. We can use the SetValidate( ) function in a script to set validation rules dynamically (at run time) in a script for DW.

16. What is the difference between a DataWindow control and object?

Datawindow control is a container for a DW object and is placed on the window.

DW control has attribute and functions.

Datawindow object is a PB object which has connection to database and GUI.

DW object has attributes. Datawindow object represents the data source. It encapsulates your database access into a high level object that handles the retrieval and manipulation of data use for displaying data and capturing user input. Datawindow object consist of :

data intelligence (perform test validation rules)

user interface (presentation style)

It is used to display data or capture user input. DW is an object that we use to retrieve, present and manipulate data from a relational DB or other data source in an intelligent way. (The DW control is the container for the DW object. The DW object is created using the DW painter; a DW control is placed on the window. A DW object has attributes. A DW control has attributes and functions. A DW object represents the data source. It encapsulates your database access into a high level object that handles the retrieval and manipulation of data. It is used for displaying data and capturing the user input. A DW object consists of data intelligence (performs test validation rules) and user interface (presentation style)

17. What are the strongest points of using the DataWindow control?

1. Displaying data.

2. Entering data.

3. Scrolling.

4. Reporting.

(true or false) The events for all PowerBuilder objects have action codes that can

be used to change PowerBuilder default processing for that event.

False! Action codes are a feature unique to the events for DW controls. Different events have a different number of action codes and different meanings for the same numbers.

ItemChanged event 0 — (Default) Accept the data

1 — Reject the data value

2 — Reject the data value but allow the focus to change

ItemError event 0 — (Default) Reject the data value and show a system error message

1 — Reject the data value but do not show a system error message

2 — Accept the data value

3 — Reject the data value but allow the focus to change

19. (true or false) PowerBuilder sends a request to the DBMS to perform an insert or delete operation following the call to the InsertRow( ) or DeleteRow( ) function

False! Only when a script issues the DataWindow function Update( ) and Retrieve() for the DataWindow control are the changes sent to the DBMS in order to update the DB.

20. What is the difference between SQLCA.SQLCode and the value returned by

the DBErrorCode() function?

The DBErrorCode() function (not SQLCA.SQLCode) checks the results of Database access performed by a DataWindow. We check SQLCA.SQLCode after explicitly issuing embedded SQL statements, such as Commit.

21. Which feature of the DataWindow painter greatly simplifies the creation of a report having only one group?

The easiest way to create a report that has a single group is to select the Group presentation style from the New DataWindow dialog box.

22. What can you do with a Query?

We can use queries as a Data Source for DataWindow objects. Queries provide reusable objects or segments of code.

• They enhance developer productivity since they can be coded once and reused as often as necessary.

• They provide flexibility in the development of DataWindow objects.

23. When do you need to create a Query?

A query object is an SQL Select statement that we construct using the Query painter when we need to use this Select frequently.

24. Where is a Query stored ?

In a .PBL file.

25. How do you create a DataWindow object dynamically?

We use SyntaxFromSQL() and Create() functions:

SQLCA.SyntaxFromSQL (select string, presentation string, Error string)

dw_1.Create(syntax, Error string)

dw_1.SetTransObject(SQLCA)

dw_1.Rerieve( )

To create a DataWindow dynamically we have to:

1. build a string to hold a SQL Select statement;

2. build a string to specify the presentation characteristics of the DataWindow object;

3. associate the syntax and description with an existing DataWindow control;

4. associate the DataWindow control with a transaction object, and perform a retrieval.

The DataWindow that is created exists only for the life of the DataWindow control, unless we use the LibraryImport( ) function to save it in a library. Dynamic DW objects allow us to create and modify DW objects on the fly. To create a DW dynamically, use the Create( ) function. Creating takes two arguments: the name of the DataWindow object that will be replaced by the new DW object, and the syntax for creating the new DW object. We can create the DW object syntax in a script, but it is easier to use the SyntaxFromSQL() to generate the syntax from a SELECT statement.

27. What is the purpose of the presentation string?

The presentation string holds information about the appearance of the DataWindow.

28. What kind of information can be specified in the presentation string?

We can specify six DataWindow properties in the presentation string:

DataWindow object, Presentation Style, Column, Text, Group, Title.

ls_present_str = “ ” takes the defaults from the Powersoft repository tables. These defaults cover fonts, colors, validation rules, etc.

29. Why must you specify the transaction object for a DataWindow control

after creating the DataWindow object?

The Create() function must be followed by SetTransObject() function because Create( ) destroys any previous association between the DataWindow and a transaction object. Then, we can issue a Retrieve().

30. Can you dynamically assign a DataWindow object?

Yes, using DataWindow’s control attribute “DataObject”.

DataWindow control has the attribute DataObject. If we want to change an associated DataWindow object at runtime we need to put a line in the script that changes the value of the DataObject attribute.

For example:

dw_1.DataObject = “d_name”

31. Let’s say, you share two DW buffers and the primary DW has some DDDW columns. Will this DDDW be shared automatically as well?

NO. After we have shared 2 DataWindows, we have to share all DropDowns as well. First, we have to get the reference for the Child DataWindow using GetChild( ) function and then do sharing by using ShareData() function.

DataWindowChild dwc_1, dwc_2

dw_1.getchild(“employee”, dwc_1)

dwc_1.SetTransObject(sqlca)

dwc_1.Retrieve( )

dw_2.getchild(“employee”,dwc_2)

dwc_1.ShareData(dwc_2)

32. How can you update multiple DataBase tables from one DataWindow?

Using Modify() function. When a DataWindow is based on a join of multiple tables, we can update all of those tables by modifying attributes DataWindow.Table, UpdateTable and column attributes Update and Key using Modify() function. For example, if the data initially came from DEPARTMENT and EMPLOYEE tables, and DEPARTMENT table was specified as an Update Table when we painted the DataWindow, we need to:

Refer Modify Method (Datawindow) Help

1. Update the DEPARTMENT table using the Update() function:

iRet = dw_1.Update (TRUE (AcceptText(), FALSE (ResetBuffer))

2.Modify the Update characteristics of the DataWindow to point to the Employee table:

IF iRet = 1 THEN

dw_1.Modify(“Dep_id.Update = NO”)

dw_1.Modify(“Dep_name.Update = NO”)

dw_1.Modify(“Dep_id.Key = NO”)

dw_1.Modify(“DataWindow.Table.Updatetable = ‘employee’“)

dw_1.Modify(“Dep_id.Update = YES”)

dw_1.Modify(“Dep_name.Update = YES”)

dw_1.Modify(“Dep_id.Key = YES”)

dw_1.Update( )

END IF

Update Embedded SQL

33. What is the method to validate a numeric column in a DataWindow?

SetValidate( )

34. In what attribute of the Transaction object are the database-specific error codes for Connect/Update/Retrieve stored?

SQLDBCode

35. How can you change a Select statement of the DataWindow at runtime?

We can change the select statement by using functions SetSQLSelect( ) or by changing the data attributes Table.Select by calling function Modify().

Modify() is preferable because it works faster.

dw_1.Modify(“datawindow.Table.Select = ‘Select * from customer’”)

Limitations to using SetSQLSelect

Use SetSQLSelect only if the data source for the DataWindow object is a SQL SELECT statement without retrieval arguments and you want PowerBuilder to modify the update information for the DataWindow object:

dw_1.Modify(“DataWindow.Table.Select=’select…'”)

Modify will not verify the SELECT statement or change the update information, making it faster but more susceptible to user error. Although you can use Modify when arguments are involved, it is not recommended because of the lack of checking.

36. What is an Update flag?

We use them when we need to update multiple DataBase tables from one DataWindow.

37. What is the difference between nested and composite reports?

In a nested report each report has its own data source.

Composite report does not have its own data source-it is just a container for other reports.

38. You have 5 DWs with DDDWs in each of them. How can you open all DDDWs at the same time? Using an array.

39. After the data has been retrieved, how can you find out the status of rows ?

By using GetUpdateStatus( ) (became obsolete and replaced by row in DBError event)

Status could be a) NewModified — Row only

b) Modified — Column

c) New – Row only

4. NotModifed Row and Column

40. Modification status – how many of them do you know and which one refers to rows only or to column only?

New and NewModified—Row only

NotModified—Row and Column

Modified—Column

41. What functions do you use to change the row status?

dw_1.SetUpdateStatus( ) …dw_1.SetItemStatus()

dw_1.GetUpdateStatus( ) dw_1.GetItemStatus()

42. How do you stop the user from editing data that is displayed in a field of a DataWindow?

Change the tab value of the field to zero in the DataWindow painter.

43. The Where clause in a SQL statement has the effect of pairing down the number of rows returned to the client from the server. How can the number of rows be reduced on the client within PowerBuilder? Use a Filter.

44. In order to sort the contents of a DataWindow, two commands must be used.

What are they and what does each do?

SetSort() and Sort().

SetSort() defines the sort criteria (primary, secondary sort files – ascending or descending order, etc.).

Sort() performs the actual sort.

45. What is the difference between computed columns and computed fields in a DataWindow object?

Computed columns are created as a result of a SQL query on the server side.

Computed fields–as a result of internal processing by DataWindow on the client side.

46. When you implement incremental search, there is no Current row, so how do you highlight the row you are looking for?

SelectRow( )

ll_row = Find( )

if ll_row > 0 then SelectRow (ll_row)

47. Explain how you understand the process of deleting data from DataWindows and Databases?

DataWindow delete puts its records into the deleted buffer of the Datawindow.

DataBase delete deletes records from a table of our database completely.

48. What are Extended column attributes? How can you change them dynamically?

It’s DataWindow object property (Expressions) which we can change dynamically using Modify() function.

49. What is a code table?

Specifies whether PowerBuilder uses the code table for the column to validate data. Values are Boolean: True—Uses code table to validate data; False—Does not use code table to validate data. The appearance of the text is specified by the edit mask. Each row in the Code Table is a pair of corresponding values: a display value that user sees and data values—those that are saved in the database.

Code Tables are used with DropDownListBox and RadioButtons.

50. How can you modify a code table during execution?

Using GETVALUE() and SETVALUE() functions.

Reports

51. In a nested report, how can the two reports be related to each other?

They are usually related by arguments or by criteria.

52. How can you pass arguments to a report nested inside a composite report?

To pass arguments to component report in a composite report, we define matching

arguments for the composite report and relate these to the arguments of the components report.

53. If you wanted to specifically reference a report nested inside a composite

report, for example, to retrieve or share data, how would you do it?

We can use retrieval arguments with a composite report to control the rows retrieved for each report:

1. Define one or more retrieval arguments for the component reports.

2. Right-click the composite report, choose Retrieval Arguments from the properties sheet and add to the composite report every argument that is needed for the component reports.

3. Right-click each component report with arguments to display the properties dialog box.

In the Arguments tab, relate each argument in the component report to an argument in the composite report. We can use DataWindow property expressions to refer to the properties of objects in a nested report.

54. What is the difference between Print() and PrintDataWindow() functions?

Print() sends the contents of a DW control or DataStore object to the printer as a print job.

PrintDataWindow (PrintJobNumber, dwcontrol) prints the contents of a DataWindow control as a print job.

PrintJobNumber—The number the PrintOpen function assigned to the print job

dwcontrol—The name of the DataWindow control or child DataWindow containing the DW object you want to print

Return value: Integer. Returns 1 if it succeeds and -1 if an error occurs. If any argument’s value is NULL, PrintDataWindow returns NULL.

55. What is a ChildDataWindow, a DropDownDataWindow? Difference?

DropDownDataWindow is an edit style for DataWindow column. It is like a DDLB which has connection to the database.

ChildDataWindow is a regular, physical, real DataWindow for an edit style DDDW. (It is a DDDW in a DW object). A combination box that combines the features of a DW object and an SLE. The DataWindow portion of the DDDW behaves like an LB but is populated from a DW object. A Child DW object is a DDDW in a DW object. A DDDW behaves as a child window of the DW object that contains them. To use a Child DW, use dwGetChild() function to obtain the child (data type DataWindowChild), assign it a transaction object, and then populate it. For example:

DataWindowChild dwc

dw_emp.GetChild(“emp_id”, dwc) // dwgetchild( ) becomes obsolete in pb 5

dwc.SetTransObject(SQLCA)

dwc.Retrieve(“argument”)

56. How do you get the name of a DropDownDataWindow? GetChild( )

57. How do you trap errors from the DataBase in the DataWindow?

Write some code in the DBError Event

For example:

if SQLCA.SQLCode <> 0 then

MessageBox( )

return 1

end if

58. What two types of computed columns are allowed in a DataWindow?

One from the database side

One from the client side

59. What is IF( ) function? (Hint: used in the DataWindow)

IF( ) function evaluates a condition and returns a value based on that condition.

60. How could you link two DataWindows having Master/Detail relationship?

Let’s say we have 2 DataWindows in an application’s window. One is just a list of employees and another contains more detailed personal info on the selected employee. To link these two DWs, we could place, for example, in the script for the first DataWindow’s DoubleClicked event, functions to retrieve the detailed info for the selected employee. We would call the Retrieve() function for the second DW with a retrieval argument which is selected in the first DataWindow Employee ID.

Data in the Detail DataWindow gets retrieved based on the retrieval argument taken from the selected row of the Master DataWindow by using function GetItemX( )

Int li_emp_num

li_row_num = dw_emp_list.GetClickedRow()

if li_row_num > 0 then

dw_emp_detail.Retrive(dw_emp_list.GetItemNumber(li_row_num, “emp_id”))

To link two DataWindows we could place, for example, in Double Clicked event function to retrieve the detailed information for selected employee.

Row = dw_1.GetRow( )

dw_emp.Retrieve(row)

and row is retrieval argument for dw_emp.

To link two DataWindows we have to retrieve data based on a retrieval argument taken from a selected row of the Master DataWindow by using function GetItemX( ), depends on data type.

61. How can you set the DataWindow to a particular row?

If you mean that a row is in the DW buffer and not on the display, I would use the ScrollToRow( ) function. If I need to make some row current, I will use SetRow( ).

long row

dw_name.SetRow(row)

dw_name.ScrollToRow(row)

62. How can you print multiple DataWindows?

We should open the print job by calling the PrintOpen( ) function. After that, we can print DWs by using PrintDataWindow( ) function. After that, we close the print job by calling PrintClose( ). When we use PrintDataWindow( ) with PrintOpen( ) and PrintClose( ), we can print several DataWindows in one print job. The info in each DataWindow control starts printing on a new page. Example:

long job

job = PrintOpen( ) //Each DataWindow starts printing on a new page.

PrintDataWindow(job, dw_EmpHeader)

PrintDataWindow(job, dw_EmpDetail)

PrintDataWindow(job, dw_EmpDptSum)

PrintClose( )

63. How many tables can be updated at the same time in a DW?

One is updated by default. If we want to update multiple tables from DW, we have to write a script for this using MODIFY().

64. Explain how a DW generates SQL select statement for each row after issuing ‘update’ function?

65. When do you use Quick Select for Data source?

If the data is coming from one table and we need only to choose columns selection criteria and sorting, we can choose Quick Select.

66. When do you use SQL Select for data source?

If we want to join tables to use retrieval arguments, or to Group data.

67. When do you choose ‘external’ for the data set and what do you have to define in this case?

If the data is not coming from the DB, for example, DW will be populated from the script (using SetItem() function) or imported from an external file (using Import file() function), we have to define the result set for DW object to type and size column in the result set.

What do you use computed fields for?

We use computed fields if we need some calculation based on column data that change for each retrieved row, some summary statistics system information (as current date and time).

69. What are the rules for update tables in the Datawindow?

If the DW contains columns from one table, PB defines all columns of this table as updatable by default. If the DataWindow contains columns from more than one table, all these tables by default are not updatable. We can modify this in the DW painter and define only one table as updatable. If we want to update multiple tables from DW, we have to write a script for this using MODIFY().

70. How do you control the update in multi-user environment?

If users are accessing the same table at the same time, we need to decide when to allow our application to update the Database. We use the Check-In and Check-Out procedures.

71. How do you assign the transaction object to the DW control?

We use SETTRANS() or SETTRANSOBJECT(). When we use SETTRANS(), the DW control uses its own Transaction object and automatically performs connect, disconnect, commit and rollback. The SetTransObject() tells the DW control to share the transaction object with other DW controls. We have to control the database processing and we are responsible for managing database transactions. Application performance is better when we use SetTransObject().

72. How do you stop the retrieval of the DW immediately? Use DBCancel()

73. If the source for a DW is a stored procedure and this stored procedure has parameters, where do we have to pass these parameters? In the RETRIEVE()

74. What are 3 buffers used by a DataWindow object?

Officially, there are 3 buffers:

Primary – data that have been modified but has not been deleted or filtered out.

Filter – data that was filtered out.

Delete – data deleted from DataWindow object.

4^th– Original– the buffer that keeps the original data from the Database.

76. What is the BLOB data type?

Unbound data type that stands for binary large object. Usually used to hold pictures in database, window’s wave sound file or MIDI music.

77. Can you call batch SQL from your DataWindow? YES.

Debugging and running an application

1. What can you do in Debug mode?

We can insert stops or a single stop through the code and display the contents of variables.

2. How can you look at instance variables in debug mode?

Instance variables are part of an object’s definition so PB lists instance variables as attributes of that object itself at the end of the list.

3. If a serious error occurs during execution, what event will be triggered?

System Error event will be triggered in the application object and we can write a script for this event.

DW Functions

1. Explain the difference between SetTrans() and SetTransObject()?

SetTransObject( ) works faster because it doesn’t perform Connect and Disconnect each

time we call it. When we specify SetTrans( ) system Does all transaction Automatically. When we specify SetTransObject( ) we have to manage all Transaction by ourselves. When we use SetTrans( ) in a script, the DataWindow uses its internal transaction object and automatically connects and disconnects as needed; any errors that occur cause an automatic rollback. Use SetTrans( ) when we want PowerBuilder to manage the database connections automatically because we have a limited number of available connections or will be used the application from a remote location. SetTrans( ) is appropriate when we are only retrieving data and do not need to hold database locks on records the user is modifying. However, for better performance, we should use SetTransObject( ).

2. When would you use SetTrans( )?

We use SetTrans() when only a limited No. of connections to the DB is allowed or we are only retrieving data and do not need to hold DB locks on records the user is modifying.

3. Explain SetActionCode(). Do DW events support this function?

The SetActionCode() function changes the action that follows a DW event. This function overrides the standard behavior of an event. Not all DW events have action codes, only those that can have different outcomes. In PB5 SetActionCode() became obsolete. We use key word “return” from 0 to 3 depending on the event. Default is (0). Return must be the last line in a script or statement.

4. How do you use ShareData() between two different DataWindows?

If we want to share the data between 2 DW controls we use dw_1.ShareData(dw_2).

Two DataWindows must have the same select but may have a different display.

In PB5 I use it with DataStore. The controls do not share formatting; only the data is shared, including data in the primary, delete, and filter buffers, and the sort order.

To turn off the sharing of data buffers for DataWindow controls we use the function dw_1.ShareDataOff(dw_2) .

5. What is the difference between TriggerEvent( ) and PostEvent( )?

TriggerEvent ( ) function makes the event occur immediately. This function does not return until the processing for the event is complete.

PostEvent( ) function makes the event occur when the current event is finished executing. In other words, it stands in the queue. The difference between them lies in timing.

6. What is the purpose of Yield( ) function?

We use YIELD( ) to allow the user to interrupt a tight loop in order to receive any messages there may be. We must call Yield( ) and check for an interruption each time we pass through the loop. We must also close the script when we close the window. Yield( ) checks the message queue and if there are message in the queue, it pulls them from the queue. Yields control to other graphic objects including objects that are not PowerBuilder. Include Yield( ) within a loop so that other processes can happen. E.g., use Yield( ) to allow end users to interrupt a loop. By yielding control, we give the user time to click on a cancel button in another window. We can also use Yield( ) in a loop in which we are waiting for something to finish so that other processing can take place, in either our or some other application.

7. What is the purpose of AcceptText( ) function?

The AcceptText( ) function validates the last item in the DataWindow control that a user worked on. Never call AcceptText( ) in the ItemChanged event. If a user enters the data and wants to close the window without pressing the tab or the update command button, we have to be responsible for saving the last modification: dwcontrol.AcceptText( )

When a user moves from item to item in a DW control, the control validates and accepts

data the user has edited. When a user modifies a DW item then immediately changes focus to another control in the window, the DW control does not accept the modified data—the data remains in the edit control. Use the AcceptText function in this situation to ensure that the DW object contains the data the user edited. A typical place to call AcceptText( ) is in a user event that is posted from the DataWindow’s LoseFocus event.

(Applies the contents of the DataWindow’s edit control to the current item in the buffer of a DataWindow control or DataStore. The data in the edit control must pass the validation rule for the column before it can be stored in the item.

Applies to DataWindow controls, DataStore objects, and child DataWindows

Syntax dwcontrol.AcceptText ( )

Argument Description

dwcontrol The name of the DataWindow control, DataStore, or child DataWindow in which you want to accept data entered in the edit control

Return value Integer. Returns 1 if it succeeds and -1 if it fails (for example, the data did not pass validation). If dwcontrol is NULL, AcceptText returns NULL.

Usage: When a user moves from item to item in a DataWindow control, the control validates and accepts data the user has edited. When a user modifies a DataWindow item then immediately changes focus to another control in the window, the DataWindow control does not accept the modified data—the data remains in the edit control. Use the AcceptText function in this situation to ensure that the DataWindow object contains the data the user edited. A typical place to call AcceptText is in a user event that is posted from the DataWindow’s LoseFocus event.

AcceptText in the ItemChanged event

Calling AcceptText in the ItemChanged event has no effect.

Events: AcceptText may trigger an ItemChanged or an ItemError event.)

8. When do you use AcceptText()?

Sometimes if user changed the data and immediately changed the focus the data is not accepted yet. We have to use AcceptText() in the ItemChange event to accept the data.

9. You want to know how fast your code is being executed.

How do you time execution of your code?

use CPU( ) function

Long. Returns the number of milliseconds of CPU time elapsed since the start of your PowerBuilder application.

These statements determine the amount of CPU time that elapsed while a group of statements executed:

Long ll_start, ll_used // Declare start and used as long integers.

ll_start = CPU( ) // Set the start equal to the current CPU usage.

… // Executable statements being timed

// Set used to the number of CPU seconds

// that were used (current CPU time – start).

ll_used = CPU( ) – ll_start

10. What is the purpose of Describe( ), Modify( )?

Modify( ) and Describe( ) functions are DW object level functions. Describe( ) reads the attributes of a DW object at runtime. Modify( ) changes the attributes at runtime.

Typical uses for Modify () are:

· Changing colors, text settings, and other appearance settings of objects

· Changing the update status of different tables in the DW so that you can update more than one table

· Modifying the WHERE clause of the DataWindow object’s SQL SELECT statement

· Turning on Query mode or Prompt For Criteria so users can specify the data they want

· Changing the status of Retrieve Only As Needed

· Changing the data source of the DataWindow object

· Controlling the Print Preview display

· Deleting and adding objects, for example, lines or bitmaps, in the DataWindow object

dw_customer.Modify(“DataWindow.Color = 255”)

where “DataWindow.Color = 255” is modstring.

Use Describe( ) to understand the structure of a DataWindow.

Typical uses for Describe () are:

• bands the DataWindow uses

• data types of the columns.

• to find out the current value of a property and use that value to make further modifications.

• to obtain the DataWindow’s SELECT statement in order to modify it (for example, by adding a WHERE clause).

dw_1.Describe(“salary.ColType”)

where “salary.ColType” is attribute list

11. How can you find out what object is under the mouse pointer in a DataWindow?

Using ObjectAtPointer( ) function that finds out where the user clicked in a graph. ObjectAtPointer() reports the region of the graph under the pointer and stores the associated series and data point numbers in the designated variables. Applies to graph controls in windows and user objects, and in DataWindow controls.

13. What is the difference between GetText() and GetItem()? Get Text() gives you the content of the text control , when the data is not accepted yet and you can use it for example in ItemChanged Event to obtain the data that did not pass validation rule. GetItem() gives you value that accepted and is in the DW buffer already.

14. How can you copy data from one DW to another if they have the same structure?

We could use the function RowsCopy() The function copies a range of rows from one DataWindow control (or DataStore object) to another, or from one buffer to another within a single DataWindow control (or DataStore). Uses for RowsCopy() include:

• Making copies of 1 or more rows so that users can create new rows based on existing data.

• Printing a range of rows by copying selected rows to another DW and printing the second DW.

dw_1.RowsCopy(dw_1.GetRow(), dw_1.RowCount(), Primary!, dw_2, 1, Primary!)

15. What is the function of Find( ) ?

Finds the next row in a DW in which data meets a specified condition.

Find (expression, start, end). The search is case-sensitive. When you compare the text to the value in a column, the case must match.

16. What is the function of SetTabOrder( )?

Changes the tab sequence number of a column in a DW control to the specified value. E.g., dwcontrol.SetTabOrder (column, TabNumber)

Use SetTabOrder( ) to change a column in a DW object to read-only by changing the tab sequence number of the column to 0.

17. What is the function of DeleteRow( )?

Deletes a current row from a DW control or Child DataWindow.

dwcontrol.DeleteRow (row)

DeleteRow( ) deletes the row from the DataWindow’s primary buffer.

18. How can you override a PB function, e.g., DeleteRow( ), for a DW control?

We need to create a User Object of the DataWindow type and declare the DeleteRow( ) function for this object having the same parameters as PowerBuilder’s DeleteRow( ). When we call the function, PB tries to find this function on the object level first, that’s why our function will be executed and not PowerBuilder’s. But we can still call PowerBuilder’s DeleteRow( ) by using Call Super :: DeleteRow( )

19. What is the function of DBErrorCode( )?

Reports the database-specific error code that triggered the DB Error event.

DBErrorCode() is obsolete. The DB error code is available as an argument SQLDBCode in the DB Error event: dwcontrol.DBErrorCode ( )

When a DB error occurs while a DW control is interacting with the DB, PB triggers the DB Error event. Since DBErrorCode is meaningful only if a DB error has occurred, we should call the function only in the DB Error event.

20. What is the function of DBErrorMessage( )?

Reports the database-specific error message that triggered the DB Error event.

DBErrorMessage( ) is obsolete. The DB error message is available as an argument SQLErrText in the DB Error event. dwcontrol.DBErrorMessage( )

When a DB error occurs while a DW control is interacting with the DB, PB triggers the DB Error event. Since DBErrorCode is meaningful only if a DB error has occurred, we should call the function only in the DB Error event.

21. What is the function of ScrollToRow( )?

Scrolls a DW control to the specified row. ScrollToRow( ) changes the current row. dwcontrol. ScrollToRow( row )

After we call ScrollToRow( ), the specified row becomes the new current row. If that row is already visible, the displayed rows do not change. If it is not visible, the displayed rows change to display the row. ScrollToRow( ) does not highlight the row. Use SelectRow( ) to let the user know what row is current. ScrollToRow( ) may trigger these events:

• ItemChanged

• ItemError

• ItemFocusChanged

• RowFocusChanged

23. What is the function of SetFilter( )?

Specifies filter criteria for a DW control.