IN Subquery

With the IN subquery, more than one row that satisfies the IN or NOT IN condition can be returned, but only one column can be returned.

This example shows the use of a NOT IN subquery in a SELECT statement: 
SELECT DISTINCT customer_num FROM orders
   WHERE order_num NOT IN
      (SELECT order_num FROM items
         WHERE stock_num = 1);

For additional information, see the IN Condition.