MySQL 5.7 Release Notes
Within the body of a stored routine (procedure or function) or a
trigger, the value of
LAST_INSERT_ID() changes the same
way as for statements executed outside the body of these kinds of
objects (see Section 12.15, “Information Functions”). The effect
of a stored routine or trigger upon the value of
LAST_INSERT_ID() that is seen by
following statements depends on the kind of routine:
If a stored procedure executes statements that change the value of
LAST_INSERT_ID(), the changed value is seen by statements that follow the procedure call.For stored functions and triggers that change the value, the value is restored when the function or trigger ends, so following statements do not see a changed value.