MySQL 5.7 Release Notes
{DEALLOCATE | DROP} PREPARE stmt_name
To deallocate a prepared statement produced with
PREPARE, use a
DEALLOCATE PREPARE statement that
refers to the prepared statement name. Attempting to execute a
prepared statement after deallocating it results in an error. If
too many prepared statements are created and not deallocated by
either the DEALLOCATE PREPARE statement or the
end of the session, you might encounter the upper limit enforced
by the max_prepared_stmt_count
system variable.
For examples, see Section 13.5, “Prepared Statements”.