Syntax:
ALTER PROCEDURE proc_name [characteristic ...]

characteristic:
    COMMENT 'string'
  | LANGUAGE SQL
  | { CONTAINS SQL | NO SQL | READS SQL DATA | MODIFIES SQL DATA }
  | SQL SECURITY { DEFINER | INVOKER }

This statement can be used to change the characteristics of a stored
procedure. More than one change may be specified in an ALTER PROCEDURE
statement. However, you cannot change the parameters or body of a
stored procedure using this statement; to make such changes, you must
drop and re-create the procedure using DROP PROCEDURE and CREATE
PROCEDURE.

You must have the ALTER ROUTINE privilege for the procedure. By
default, that privilege is granted automatically to the procedure
creator. This behavior can be changed by disabling the
automatic_sp_privileges system variable. See
http://dev.mysql.com/doc/refman/5.7/en/stored-routines-privileges.html.

URL: http://dev.mysql.com/doc/refman/5.7/en/alter-procedure.html

