EXISTS and NOT EXITS

                                                          These are for use only with sub queries and produce simple true/false results.EXITS is true if and only it there exits at least one row in the result table returned by the sub query ,and false if the sub query returns an empty  result table.NOT EXITS is the opposite of  EXITS. Since these check only for existence/non-existence of rows in the sub query result table,the sub query can contain any number of columns 


Example of EXITS


SELECT columns
FROM tables
WHERE EXISTS ( subquery );


Example of NOT-EXITS
SELECT *
FROM suppliers
WHERE not exists (select * from orders Where suppliers.supplier_id = orders.supplier_id);


The EXISTS condition can be used in any valid SQL statement - select, insert, update, or delete.