Specifying a System Descriptor Area (ESQL/C)

If you do not know the number of parameters to be supplied at runtime or their data types, you can associate input values from a system-descriptor area. A system-descriptor area describes the data type and memory location of one or more values to replace question-mark ( ? ) placeholders.

A system-descriptor area conforms to the X/Open standards.

Use the SQL DESCRIPTOR keywords to introduce the name of a system descriptor area as the location of the parameters.

The COUNT field in the system-descriptor area corresponds to the number of dynamic parameters in the prepared statement. The value of COUNT must be less than or equal to the number of item descriptors that were specified when the system-descriptor area was allocated with the ALLOCATE DESCRIPTOR statement. You can obtain the value of a field with the GET DESCRIPTOR statement and set the value with the SET DESCRIPTOR statement.

The following example shows the OPEN ... USING SQL DESCRIPTOR statement:
EXEC SQL allocate descriptor 'desc1';
EXEC SQL open selcurs using sql descriptor 'desc1';

As the example indicates, the system descriptor area must be allocated before you reference it in the OPEN statement.