如何合并两个select mysql查询的结果[重复]

Posted 2023-02-24

【中文标题】如何合并两个select mysql查询的结果[重复]

【英文标题】：How to merge the result of two select mysql query [duplicate]

【发布时间】：2021-11-09 12:58:47

【问题描述】：

我的第一个查询是

select GEAR,count(GEAR) 
from new_failure 
where STN_CODE = "BVH" group by(Gear);

它的结果是

图片不可见时的结果

# GEAR  Total
SIGNAL  8
POINT   16
HASSDAC 5
,SIGNAL 1
SSDAC   1
TRACK CIRCUIT   9
UFSBI   2
DC  1

第二次查询

select GEAR,count(GEAR) 
from new_failure 
where STN_CODE = "BVH"  
and MONTH(fail_time) = 4 
group by(Gear);

结果

# GEAR  April
SIGNAL  3
POINT   4
HASSDAC 1
,SIGNAL 1
SSDAC   1

我希望结果如下图所示

【问题讨论】：

请查看***.com/questions/10538539/…

select t1.Gear, t1.[This],COALESCE(t2.[April],0) AS [ April] from (select GEAR,count(GEAR) as "This" from new_failure where STN_CODE = "BVH" group by(Gear)) t1 LEFT JOIN (select GEAR,count(GEAR) as "April" from new_failure 其中STN_CODE = "BVH" and MONTH(fail_time) = 4 group by(Gear)) t2 on (t1 .Gear = t2.Gear);我的查询看起来像这样，但在 t1 出现错误。[this] "[" is not valid

【参考方案1】：

您可以使用 LEFT JOIN、RIGHT JOIN 或 JOIN，具体取决于您的目标是什么，

SELECT * 
FROM ( select GEAR,count(GEAR) 
       from new_failure 
       where STN_CODE = "BVH" group by(Gear) AS A
JOIN ( select GEAR,count(GEAR) 
       from new_failure 
       where STN_CODE = "BVH"  
       and MONTH(fail_time) = 4 AS B
ON A.orders_id=B.orders_id

或者您可以参考此链接了解类似问题 joining two select statements

【讨论】：

此解决方案不必要地过于复杂，因为两个查询都从同一个表中选择数据并按同一字段分组。唯一的区别是要计算什么，这可以通过条件计数来完成。表上的单次传递，没有连接。