Optimizer Directives

The Optimizer Directives segment specifies keywords that you can use to partially or fully specify the query plan of the optimizer. Use this segment whenever you see a reference to Optimizer Directives in a syntax diagram.

Syntax

Optimizer Directives:
 
|--+- --+-+----------------------------------------------------->
   +-{+---+
   '-/*+--'
 
   .-,------------------------------------------------.
   V                                (1)               |
>----+-| Access-Method Directives |-----------------+-+--------->
     |                          (2)                 |
     +-| Join-Order Directive |---------------------+
     |                            (3)               |
     +-| Join-Method Directives |-------------------+
     |  (4)                                    (5)  |
     +--------| Optimization-Goal Directives |------+
     |                             (6)              |
     +-| Explain-Mode Directives |------------------+
     |  (7)                                 (8)     |
     '--------| Rewrite Method Directives |---------'
 
>--+-----+------------------------------------------------------|
   +-}---+
   '- */-'

Notes:

Usage

Optimizer directives are valid in any query of a DELETE, SELECT, or UPDATE statement. Use one or more directives to partially or fully specify the query plan of the optimizer. The scope of the directive is the current query only.

Directives are enabled by default. To obtain information about how specified directives are processed, view the output of the SET EXPLAIN statement. To disable directives, set the IFX_DIRECTIVES environment variable to 0 or OFF, or set the DIRECTIVES parameter in the ONCONFIG file to 0.