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A section consists of ALLBASE/SQL instructions for executing an
SQL command.
The SQL commands that do not generate stored sections are listed in
the "Stored Sections" paragraph of the "Using the ALLBASE/SQL COBOL
Preprocessor."
Not every SQL command requires a section. For
each SQL command that does require a section, the preprocessor
creates the section and assigns to it a unique reference number.
In the following preprocessor generated code SQLSECNUM contains
the number of the stored section.
MOVE 1 TO SQLSECNUM
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CALL SQLXCBL USING SQLXFET, SQLCA, SQLOWNER, SQLMODNAME,
SQLSECNUM, SQLTEMPV, SQLINLEN, SQLOUTLEN, SQLTRUE
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Purpose of Sections | |
A section serves two purposes:
Access validation: Before executing a stored section at run
time, 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.
Runtime performance is improved by creating and storing sections
at preprocessing time rather than at run time. 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: Change in authorities of the module's owner. Alteration to tables accessed by the program. Deletion or creation of indexes. Update of a table's statistics.
At run time, ALLBASE/SQL executes valid sections and attempts to
validate any section 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. When a section is validated at run time, it remains in the valid
state until an event that invalidates it occurs. The program
execution during which validation occurs is slightly slower than
program executions following validation. |
