Exits a function or procedure unconditionally, optionally providing a return value. Statements following RETURN are not executed.
RETURN [ ( expression ) ]
Within a function, the expression should be of the same data type as the RETURN data type of the function.
CREATE FUNCTION product ( a numeric,
                b numeric ,
                c numeric)
RETURNS numeric
BEGIN
  RETURN ( a * b * c ) ;
END
            SELECT product (2, 3, 4)
product (2,3,4) 24
CREATE PROCEDURE customer_products
( in customer_id integer DEFAULT NULL)
RESULT ( id integer, quantity_ordered integer )
BEGIN
  IF customer_id NOT IN (SELECT ID FROM Customers)
  OR customer_id IS NULL THEN
    RETURN
  ELSE
    SELECT ID,sum(
      SalesOrderItems.Quantity )
    FROM Products,
        SalesOrderItems,
        SalesOrders
    WHERE SalesOrders.CustomerID = customer_id
    AND SalesOrders.ID = SalesOrderItems.ID
    AND SalesOrderItems.ProductID = Products.D
    GROUP BY Products.ID
  END IF
END
            RETURN is used in procedures for Transact-SQL-compatibility, and is used to return an integer error code.