The EXISTS operator tests a subselect for the existance of one or more rows.

The EXISTS operator returns a TRUE value:
> when even one row in a subselect matches the value comparison in the subselect.

The EXISTS operator returns a FALSE value:
> when no rows in a subselect match the value comparison in the subselect.

The NOT EXISTS operator returns a TRUE value:
> when no rows in a subselect match the value comparison in the subselect.

The NOT EXISTS operator returns a FALSE value:

> when even one row in a subselect matches the value comparison in the subselect.

     Format:      SELECT select_columns
                         FROM tables
                       WHERE [NOT] EXISTS (subselect);

> DB2, MySQL, Oracle, Postgre SQL, and SQL Server support EXISTS.