The Stored Section

A section consists of ALLBASE/SQL instructions for executing an SQL command. The preprocessor creates a section for each SQL command embedded in a program except for the following commands:

   BEGIN DECLARE SECTION             INCLUDE

   BEGIN WORK                        OPEN

   CLOSE                             PREPARE

   COMMIT WORK                       RELEASE

   CONNECT                           ROLLBACK WORK

   DECLARE CURSOR                    SAVEPOINT

   DELETE WHERE CURRENT              START DBE

   DESCRIBE                          STOP DBE

   END DECLARE SECTION               SQLEXPLAIN

   EXECUTE                           TERMINATE USER

   EXECUTE IMMEDIATE                 UPDATE WHERE CURRENT

                                     WHENEVER

The preprocessor assigns a number to each section and references the appropriate stored section in the generated code:

   

   CALL SQLXFE(SQLAID,SQLOWN,SQLMND,1,SQLTMP,16,56,1)

Purpose of Sections

A section serves two purposes:

Access validation: Before executing a stored section at runtime, ALLBASE/SQL ensures that any objects referenced exist and that runtime authorization criteria are satisfied.
Access optimization: If ALLBASE/SQL has more than one way to access data, it determines the most efficient method and creates the section based on that method. Indexes, for example, can expedite the performance of some queries.

By creating and storing sections at preprocessing time rather than at runtime, you improve runtime performance.

Section Validity

A section is assigned one of two states at preprocessing time: valid or invalid. A section is valid when access validation criteria are satisfied. If the SQL command references objects that exist at preprocessing time and the individual doing the preprocessing is authorized to issue the command, the stored section is marked as valid. A section is invalid when access validation criteria are not satisfied. If the SQL command references an object that does not exist at preprocessing time or if the individual doing the preprocessing is not authorized to issue the command, the stored section is marked as invalid. After being stored by the preprocessor, a valid section is marked as invalid when such activities as the following occur:

Changes in authorities of the module's owner.
Alterations to tables accessed by the program.
Deletions or creations of indexes.
Updating a table's statistics.

At runtime, ALLBASE/SQL executes valid sections and attempts to validate any sections marked as invalid. If an invalid section can be validated, as when an altered table does not affect the results of a query, ALLBASE/SQL marks the section as valid and executes it. If an invalid section cannot be validated, as when a table reference is invalid because the table owner name has changed, ALLBASE/SQL returns an error indication to the application program, which in turn can determine what to do.

When a section is validated at runtime, it remains in the valid state until an event that invalidates it occurs. Program execution during which validation occurs is slightly slower than program execution following section validation.

The Stored Section

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Purpose of Sections

Section Validity