Varying-list SELECT statements

In dynamic SQL, varying-list SELECT statements are ones for which the number and format of result columns to be returned are not predictable; that is, you do not know how many variables you need, or what the data types are.

Therefore, you cannot define host variables in advance to accommodate the result columns returned.

Note: Start of changeIn REXX, steps 5.b, 6, and 7 are not applicable. REXX only supports SQL descriptors defined using the SQLDA structure; it does not support allocated SQL descriptors.End of change

If your application accepts varying-list SELECT statements, your program has to:

  1. Place the input SQL statement into a host variable.
  2. Issue a PREPARE statement to validate the dynamic SQL statement and put it into a form that can be run. If DLYPRP (*YES) is specified on the CRTSQLxxx command, the preparation is delayed until the first time the statement is used in an EXECUTE or DESCRIBE statement, unless the USING clause is specified on the PREPARE statement.
  3. Declare a cursor for the statement name.
  4. Open the cursor (declared in step 3) that includes the name of the dynamic SELECT statement.
  5. Start of changeFor an allocated SQL descriptor, run an ALLOCATE DESCRIPTOR statement to define the descriptor you intend to use.End of change
  6. Issue a DESCRIBE statement to request information from SQL about the type and size of each column of the result table.
    Notes:
    1. You can also code the PREPARE statement with an INTO clause to perform the functions of PREPARE and DESCRIBE with a single statement.

    2. If using an SQLDA and the SQLDA is not large enough to contain column descriptions for each retrieved column, the program must determine how much space is needed, get storage for that amount of space, build a new SQLDA, and reissue the DESCRIBE statement.

      Start of change If using an allocated SQL descriptor and the descriptor is not large enough, deallocate the descriptor, allocate it with a larger number of entries, and reissue the DESCRIBE statement.End of change

  7. For an SQLDA descriptor, allocate the amount of storage needed to contain a row of retrieved data.
  8. For an SQLDA descriptor, put storage addresses into the SQLDA to tell SQL where to put each item of retrieved data.
  9. Start of changeFETCH a row.End of change
  10. Process the data returned in the SQL descriptor.
  11. Handle any SQL return codes that might result.
  12. When end of data occurs, close the cursor.
  13. Start of changeFor an allocated SQL descriptor, run a DEALLOCATE DESCRIPTOR statement to delete the descriptor.End of change
Parent topic: Process SELECT statements and use a descriptor
Related reference
Example: Select-statement for allocating storage for SQLDA