Syntax
------

RETURN expr

The RETURN statement terminates execution of a stored function and returns the
value expr to the function caller. There must be at least one RETURN statement
in a stored function. If the function has multiple exit points, all exit
points must have a RETURN.

This statement is not used in stored procedures, triggers, or events. LEAVE
can be used instead.

The following example shows that RETURN can return the result of a scalar
subquery:

CREATE FUNCTION users_count() RETURNS BOOL
 READS SQL DATA
BEGIN
 RETURN (SELECT COUNT(DISTINCT User) FROM mysql.user);
END;

URL: https://mariadb.com/kb/en/return/