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 PowerBuilder 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 runtime. This is called dynamic SQL. The parameters used
in dynamic SQL statements can change each time the program is
executed.
Using SQL Anywhere
For information about using dynamic SQL with SQL Anywhere, see the
SQL Anywhere documentation.
Four formats
PowerBuilder 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 |
|
Format 2 |
Non-result-set statements with input |
|
Format 3 |
Result-set statements in which the input parameters |
|
Format 4 |
Result-set statements in which the input parameters, |
-
To handle these situations, you use:
-
The PowerBuilder dynamic SQL statements
-
The dynamic versions of CLOSE, DECLARE, FETCH, OPEN, and
EXECUTE -
The PowerBuilder 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 PowerBuilder dynamic SQL statements are:
|
1 2 3 4 5 6 7 8 9 |
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:
|
1 2 |
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:
|
1 2 |
DynamicDescriptionArea dda_desc1 dda_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:
|
1 |
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:
|
1 |
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:
|
1 2 3 4 5 6 7 8 9 10 |
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. |
Declaring a procedure with the SQL Native
Client database interface
When you connect to Microsoft SQL Server using the PowerBuilder SQL
Native Client (SNC) database interface, the syntax for declaring a
procedure is:
|
1 2 3 4 |
DECLARE logical_procedure_name PROCEDURE FOR [@rc=]procedure_name {@param1 = value1 [OUTPUT], @param2 = value2 [OUTPUT], ...} {USING transaction_object}; |
[@rc=] indicates that you want to get the procedure’s return
value.
Use the keyword OUTPUT or OUT to indicate an output parameter if you
want to get the output parameter’s value.
If the BindSPInput database parameter is 0, value1, value2,… can
be either PowerBuilder script variables or literal values. If BindSPInput
is 1, value1, value2, … must be PowerBuilder script variables. If you
specify literal values, the SNC interface returns a runtime error.
When you declare a dynamic SQL statement with a procedure, enter a
question mark (?) for each IN/OUT parameter in the statement. Value
substitution is positional. For examples, see Dynamic SQL Format 3 and
4.