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SQL Anywhere 12.0.0 » SQL Anywhere Server - SQL Usage » Query optimization and execution » Semantic query transformations


Rewriting subqueries as EXISTS predicates

The assumptions that underlie the design of SQL Anywhere require that it conserves memory and that by default it returns the first few results of a cursor as quickly as possible. In keeping with these objectives, SQL Anywhere rewrites all set-operation subqueries, such as IN, ANY, or SOME predicates, as EXISTS or NOT EXISTS predicates, if such rewriting is semantically correct. By doing so, SQL Anywhere avoids creating unnecessary work tables and may more easily identify a suitable index through which to access a table.

 Uncorrelated and correlated subqueries
 See also