Mysql 如何对两个表使用max

我想在时间字段上使用

MAX

，它可以工作，但值为“0”

此查询在我使用

MAX

之前：

SELECT a.`JAM`, AVG(a.PacketLoss) AVG
FROM (
SELECT `JAM`,`RNC`,`IPPATH_PM` AS PHB,`VS_IPPM_FORWORD_DROPMEANS` AS PacketLoss, `VSIPPMRttMeans` AS Latency, 'IPPM'
FROM `rnc_ippm_meas`
WHERE `JAM`>= CURDATE() AND `IPPATH_PM` LIKE '%AF31%'
UNION
SELECT `JAM`,`RNC`,`IPPOOL_PM`,`VSIPPOOLIPPMForwardDrop-Means`,`VSIPPOOLIPPMRttMeans`, 'IPPOOLPM'
FROM `rnc_ippool_ippm_meas` 
WHERE `JAM`>= CURDATE() AND `IPPOOL_PM` LIKE '%AF31%') a
GROUP BY a.`JAM`
LIMIT 10000 

此处输出

然后我在这里使用

MAX

SELECT a.`JAM`, AVG(a.PacketLoss) AVG
FROM (
SELECT MAX(JAM) AS JAM,`RNC`,`IPPATH_PM` AS PHB,`VS_IPPM_FORWORD_DROPMEANS` AS PacketLoss, `VSIPPMRttMeans` AS Latency, 'IPPM'
FROM `rnc_ippm_meas`
WHERE `JAM`>= CURDATE() AND `IPPATH_PM` LIKE '%AF31%'
UNION
SELECT MAX(JAM) AS JAM,`RNC`,`IPPOOL_PM`,`VSIPPOOLIPPMForwardDrop-Means`,`VSIPPOOLIPPMRttMeans`, 'IPPOOLPM'
FROM `rnc_ippool_ippm_meas` 
WHERE `JAM`>= CURDATE() AND `IPPOOL_PM` LIKE '%AF31%') a
GROUP BY a.`JAM`
LIMIT 10000

---

我希望输出的是上次的值，有人能帮我吗？谢谢

您需要在外部查询中使用

MAX

，而不是内部查询。在进行内部查询时，MySQL会为非聚合列提供一个不确定的值，例如，

VS_IPPM\u FORWORD\u DROPMEANS

，对于示例数据，该值似乎为0。将查询更改为：

SELECT MAX(a.`JAM`), AVG(a.PacketLoss) AVG
FROM (
SELECT `JAM`,`RNC`,`IPPATH_PM` AS PHB,`VS_IPPM_FORWORD_DROPMEANS` AS PacketLoss, `VSIPPMRttMeans` AS Latency, 'IPPM'
FROM `rnc_ippm_meas`
WHERE `JAM`>= CURDATE() AND `IPPATH_PM` LIKE '%AF31%'
UNION
SELECT `JAM`,`RNC`,`IPPOOL_PM`,`VSIPPOOLIPPMForwardDrop-Means`,`VSIPPOOLIPPMRttMeans`, 'IPPOOLPM'
FROM `rnc_ippool_ippm_meas` 
WHERE `JAM`>= CURDATE() AND `IPPOOL_PM` LIKE '%AF31%') a

---

请注意，不再需要“分组依据”，因为您在整个数据集上使用了

MAX

和

AVG

，并且不需要

限制，因为此查询将只生成一行。
您需要在外部查询中使用
MAX
，而不是内部查询。在进行内部查询时，MySQL会为非聚合列提供一个不确定的值，例如，
VS_IPPM\u FORWORD\u DROPMEANS
，对于示例数据，该值似乎为0。将查询更改为：

SELECT MAX(a.`JAM`), AVG(a.PacketLoss) AVG
FROM (
SELECT `JAM`,`RNC`,`IPPATH_PM` AS PHB,`VS_IPPM_FORWORD_DROPMEANS` AS PacketLoss, `VSIPPMRttMeans` AS Latency, 'IPPM'
FROM `rnc_ippm_meas`
WHERE `JAM`>= CURDATE() AND `IPPATH_PM` LIKE '%AF31%'
UNION
SELECT `JAM`,`RNC`,`IPPOOL_PM`,`VSIPPOOLIPPMForwardDrop-Means`,`VSIPPOOLIPPMRttMeans`, 'IPPOOLPM'
FROM `rnc_ippool_ippm_meas` 
WHERE `JAM`>= CURDATE() AND `IPPOOL_PM` LIKE '%AF31%') a

请注意，不再需要“分组依据”

，因为您在整个数据集上使用了

MAX

和

AVG

，并且不需要

限制，因为此查询只生成一行。
@lutfimetahudin好听！如果这确实解决了你的问题，请考虑标记接受的答案（在上/下投票箭头下的复选标记）。看到@lutfimethaudin很高兴听到！如果这确实解决了你的问题，请考虑标记接受的答案（在上/下投票箭头下的复选标记）。看见