The EXISTS condition is considered "to be met" if the subquery returns at least one row.
The syntax for the EXISTS condition is:
WHERE EXISTS ( subquery );
The EXISTS condition can be used in any valid SQL statement - select, insert, update, or delete.
Let's take a look at a simple example. The following is an SQL statement that uses the EXISTS condition:
where suppliers.supplier_id = orders.supplier_id);
This select statement will return all records from the suppliers table where there is at least one record in the orders table with the same supplier_id.
Ex 2 - NOT EXISTS
The EXISTS condition can also be combined with the NOT operator.
WHERE not exists (select * from orders Where suppliers.supplier_id = orders.supplier_id);
This will return all records from the suppliers table where there are no records in the orders table for the given supplier_id.