Optimizer directives

IBM® Informix® SQL allows you to specify query optimization directives to force the query optimizer to use a different path than the implicit plan. With IBM Informix, optimizer directives are specified with the following SQL comment markers followed by a plus sign:

/*+ optimizer-directives */
{+  optimizer-directives }
--+ optimizer-directives

Genero BDL partially supports optimizer directives:

  • The static SQL syntax does not allow the C-style optimizer syntax.
  • The curly-brace and dash-dash optimizer directive syntaxes cannot be used in static SQL statements, because these correspond to the 4GL language comments.
  • However, you can execute queries with optimization directives with Dynamic SQL.
Tip: Optimization directives are not portable. If you plan to use different types of database servers, it is recommended that you avoid the usage of query plan hints.