DELIMITER $$DROP PROCEDURE IF EXISTS `test`.`pp`$$CREATE DEFINER=`root`@`localhost` PROCEDURE `pp`(IN _id int)
BEGIN
SELECT * FROM aaa LEFT JOIN bbb ON aaa.id = bbb.id WHERE aaa.id = _id;
END$$DELIMITER ;call pp(6);
BEGIN
SELECT * FROM aaa LEFT JOIN bbb ON aaa.id = bbb.id WHERE aaa.id = _id;
END$$DELIMITER ;call pp(6);
union all 不会排除重复的记录