Subquery flattening is an optimization technique in which the optimizer rewrites a query containing a subquery into a query that uses a join. Sybase IQ flattens many but not all subqueries. The new database options SUBQUERY_FLATTENING_PREFERENCE and SUBQUERY_FLATTENING_PERCENT control under what circumstances the optimizer chooses to use this optimization.
The FLATTEN_SUBQUERIES option has been deprecated in Sybase IQ 15.0.
