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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. 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.

URL: https://dev.mysql.com/doc/refman/8.0/en/return.html