mysql 使用union（all） + order by 导致排序失效

1、SQL1如下

SELECT
	aa.* 
FROM
	apas_smoke aa 
WHERE
	STATUS = 0 
	AND aa.area_id = 'd61523dda339441f80008634c6b91f60' 
	AND aa.type = '3' 
	AND to_days( create_time ) = to_days(
	now()) 
ORDER BY
	CAST( aa.smoke_number AS UNSIGNED ) ASC

查询结果如下，smoke_number 顺序为3,4

2、sql2如下：

SELECT
	bb.* 
FROM
	apas_smoke bb 
WHERE
	bb.STATUS = 0 
	AND bb.area_id = 'd61523dda339441f80008634c6b91f60' 
	AND bb.type = '1' 
	AND to_days( create_time ) = to_days(
	now()) 
ORDER BY
	CAST( bb.smoke_number AS UNSIGNED ) ASC

查询结果如下，smoke_number顺序为1,2

 3、但是当使用UNION后，SQL如下

( SELECT
	aa.* 
	FROM
		apas_smoke aa 
	WHERE
		STATUS = 0 
		AND aa.area_id = 'd61523dda339441f80008634c6b91f60' 
		AND aa.type = '3' 
		AND to_days( create_time ) = to_days(
		now()) 
	ORDER BY
		CAST( aa.smoke_number AS UNSIGNED ) ASC 
	) UNION
	(
	SELECT
		bb.* 
	FROM
		apas_smoke bb 
	WHERE
		bb.STATUS = 0 
		AND bb.area_id = 'd61523dda339441f80008634c6b91f60' 
		AND bb.type = '1' 
		AND to_days( create_time ) = to_days(
		now()) 
	ORDER BY
	CAST( bb.smoke_number AS UNSIGNED ) ASC 
	)

查询结果，如下，smoke_number顺序与3,4,2,1  与预期的顺序  3,4,1,2不一致。

**原因：union（all）会使order by失效，解决办法，加limit 

4、最终SQL 

(       
　　　　 SELECT
	        aa.* 
	FROM
		apas_smoke aa 
	WHERE
		STATUS = 0 
		AND aa.area_id = 'd61523dda339441f80008634c6b91f60' 
		AND aa.type = '3' 
		AND to_days( create_time ) = to_days(
		now()) 
	ORDER BY
		CAST( aa.smoke_number AS UNSIGNED ) ASC 
		LIMIT 2 
) 
UNION
(       SELECT
		bb.* 
	FROM
		apas_smoke bb 
	WHERE
		bb.STATUS = 0 
		AND bb.area_id = 'd61523dda339441f80008634c6b91f60' 
		AND bb.type = '1' 
		AND to_days( create_time ) = to_days(
		now()) 
	ORDER BY
		CAST( bb.smoke_number AS UNSIGNED ) ASC 
	        LIMIT 2 
)

查询结果：

 问题解决。

标签：aa,bb,union,days,number,smoke,mysql,id,order
来源： https://www.cnblogs.com/lansetuerqi/p/13986528.html