Using dynamic SQL

General information

Because database applications usually perform a specific activity, you usually know the complete SQL statement when you write and compile the script. When PocketBuilder does not support the statement in embedded SQL (as with a DDL statement) or when the parameters or the format of the statements are unknown at compile time, the application must build the SQL statements at execution time. This is called dynamic SQL. The parameters used in dynamic SQL statements can change each time the program is executed.

Using Adaptive Server® Anywhere For information about using dynamic SQL with Adaptive Server Anywhere, see the Adaptive Server Anywhere Programming Interfaces book.

Four formats

PocketBuilder has four dynamic SQL formats. Each format handles one of the following situations at compile time:

Format	When used
Format 1	Non-result-set statements with no input parameters
Format 2	Non-result-set statements 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

To handle these situations, you use:

The PocketBuilder dynamic SQL statements
The dynamic versions of CLOSE, DECLARE, FETCH, OPEN, and EXECUTE
The PocketBuilder datatypes DynamicStagingArea and DynamicDescriptionArea

About the examples The examples assume that the default transaction object (SQLCA) has been assigned valid values and that a successful CONNECT has been executed. Although the examples do not show error checking, you should check the SQLCode after each SQL statement.

Dynamic SQL statements

The PocketBuilder dynamic SQL statements are:

DESCRIBE DynamicStagingArea
	INTO DynamicDescriptionArea ;

EXECUTE {IMMEDIATE} SQLStatement
	{USING TransactionObject} ;

EXECUTE DynamicStagingArea
	USING ParameterList ;

EXECUTE DYNAMIC Cursor | Procedure
	USING ParameterList ;

OPEN DYNAMIC Cursor | Procedure
	USING ParameterList ;

EXECUTE DYNAMIC Cursor | Procedure
	USING DESCRIPTOR DynamicDescriptionArea ;

OPEN DYNAMIC Cursor | Procedure
	USING DESCRIPTOR DynamicDescriptionArea ;

PREPARE DynamicStagingArea
	FROM SQLStatement {USING TransactionObject} ;

Two datatypes

DynamicStagingArea DynamicStagingArea is a PowerBuilder datatype. PowerBuilder uses a variable of this type to store information for use in subsequent statements.

The DynamicStagingArea is the only connection between the execution of a statement and a transaction object and is used internally by PowerBuilder; you cannot access information in the DynamicStagingArea.

PowerBuilder provides a global DynamicStagingArea variable named SQLSA that you can use when you need a DynamicStagingArea variable.

If necessary, you can declare and create additional object variables of the type DynamicStagingArea. These statements declare and create the variable, which must be done before referring to it in a dynamic SQL statement:

DynamicStagingArea dsa_stage1

dsa_stage1 = CREATE DynamicStagingArea

After the EXECUTE statement is completed, SQLSA is no longer referenced.

DynamicDescriptionArea DynamicDescriptionArea is a PowerBuilder datatype. PowerBuilder uses a variable of this type to store information about the input and output parameters used in Format 4 of dynamic SQL.

PowerBuilder provides a global DynamicDescriptionArea named SQLDA that you can use when you need a DynamicDescriptionArea variable.

If necessary, you can declare and create additional object variables of the type DynamicDescriptionArea. These statements declare and create the variable, which must be done before referring to it in a dynamic SQL statement:

DynamicDescriptionArea dda_desc1

dsa_desc1 = CREATE DynamicDescriptionArea

For more information about SQLDA, see Dynamic SQL Format 4.

Preparing to use dynamic SQL

When you use dynamic SQL, you must:

Prepare the DynamicStagingArea in all formats except Format 1
Describe the DynamicDescriptionArea in Format 4
Execute the statements in the appropriate order

Preparing and describing the datatypes Since the SQLSA staging area is the only connection between the execution of a SQL statement and a transaction object, an execution error will occur if you do not prepare the SQL statement correctly.

In addition to SQLSA and SQLDA, you can declare other variables of the DynamicStagingArea and DynamicDescriptionArea datatypes. However, this is required only when your script requires simultaneous access to two or more dynamically prepared statements.

This is a valid dynamic cursor:

DECLARE my_cursor DYNAMIC CURSOR FOR SQLSA ;

PREPARE SQLSA FROM "SELECT emp_id FROM employee" ;

OPEN DYNAMIC my_cursor ;

This is an invalid dynamic cursor. There is no PREPARE, and therefore an execution error will occur:

DECLARE my_cursor DYNAMIC CURSOR FOR SQLSA ;

OPEN DYNAMIC my_cursor ;

Statement order Where you place the dynamic SQL statements in your scripts is unimportant, but the order of execution is important in Formats 2, 3, and 4. You must execute:

The DECLARE and the PREPARE before you execute any other dynamic SQL statements
The OPEN in Formats 3 and 4 before the FETCH
The CLOSE at the end

If you have multiple PREPARE statements, the order affects the contents of SQLSA.

These statements illustrate the correct ordering:

DECLARE my_cursor DYNAMIC CURSOR FOR SQLSA

string sql1, sql2

sql1 = "SELECT emp_id FROM department "&

WHERE salary > 90000"

sql2 = "SELECT emp_id FROM department "&

WHERE salary > 20000"

IF deptId = 200 then

		PREPARE SQLSA FROM :sql1 USING SQLCA ;

ELSE

		PREPARE SQLSA FROM :sql2 USING SQLCA ;

END IF

OPEN DYNAMIC my_cursor ;									// my_cursor maps to the

									// SELECT that has been

									// prepared.