MySQL 5.7 Release Notes
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. There may be more than one if
the function has multiple exit points.
This statement is not used in stored procedures, triggers, or
events. The LEAVE statement can
be used to exit a stored program of those types.