Exists predicate 

The exists predicate is used to test if a subquery returns any rows.

Syntax

<exists predicate> ::=              EXISTS '(' <query specification> ')'.

 

The result of the <exists predicate> is true if the result of the <query specification> is not empty (contains one or more rows), otherwise the result of the <exists predicate> is false.

Example

SELECT * FROM a WHERE EXISTS                 ( SELECT * FROM b WHERE b.c = 0 )

The EXISTS Predicate. This query contains an uncorrelated subquery. It returns all rows from table a if there is at least one row in table bfor which the column cof table b has the value 0.

See

Query Specification