Question

对于下面的查询，我正在尝试检索lastheatbeattime大于10的计算机列表。我希望每次运行查询时都返回相同的结果。目前，下面的代码多次检索相同的结果，然后进行更改。

我对SQL不是很有经验，所以简单的回答是可取的。

SELECT 
COUNT(*) AS TestValue,
locations.name AS IDentityField,
(SELECT c.computerid FROM computers ORDER BY c.computerid DESC LIMIT 1) AS ComputerID, 
locations.locationid AS LocationID,
acd.NoAlerts,
acd.UpTimeStart,
acd.UpTimeEnd 
FROM
Computers c 
JOIN AgentComputerData acd 
ON (c.computerid = acd.computerid) 
JOIN heartbeatcomputers 
ON c.Computerid = heartbeatcomputers.computerid 
JOIN locations 
ON c.`LocationID` = locations.`LocationID` 
JOIN v_extradatalocations 
ON c.`LocationID` = v_extradatalocations.`locationid` 
WHERE c.os LIKE '%Windows Server%' 
AND LastHeartbeatTime < DATE_ADD(NOW(), INTERVAL - 10 MINUTE) 
AND v_extradatalocations.`Server Service Plan` LIKE "%Managed 24x7%" 
AND locations.locationid != 154
GROUP BY c.`LocationID` 
HAVING COUNT(DISTINCT c.computerid) > 1 
AND COUNT(DISTINCT c.`ClientID`) < 20;

Answer 1

如果添加ORDER BY子句，则可以使结果更具确定性 - 如果没有这个，则顺序是随机的（通常与SQL可以执行查询的最快方式相关）。

Answer 2

仔细观察，你想要这样做：

SELECT
COUNT(*) AS TestValue,
locations.name AS IDentityField,
c.computerid AS ComputerID,
locations.locationid AS LocationID,
acd.NoAlerts,
acd.UpTimeStart,
acd.UpTimeEnd
FROM
Computers c
JOIN AgentComputerData acd
ON (c.computerid = acd.computerid)
JOIN heartbeatcomputers
ON c.Computerid = heartbeatcomputers.computerid
JOIN locations
ON c.`LocationID` = locations.`LocationID`
JOIN v_extradatalocations
ON c.`LocationID` = v_extradatalocations.`locationid`
WHERE c.os LIKE '%Windows Server%'
AND LastHeartbeatTime < DATE_ADD(NOW(), INTERVAL - 10 MINUTE)
AND v_extradatalocations.`Server Service Plan` LIKE "%Managed 24x7%"
AND locations.locationid != 154
GROUP BY c.`LocationID`
HAVING COUNT(DISTINCT c.computerid) > 1
AND COUNT(DISTINCT c.`ClientID`) < 20
ORDER BY c.computerid DESC;

你的嵌套选择是抓取一个随机行，因为没有任何内容可以将它与查询的其余部分联系起来。

Answer 3

答案很简单..将max（）添加到c.computerid AS ComputerID，例如。 MAX（c.computerid）AS ComputerID，

这是因为我混合了分组和未分组的列，因此sql返回“随机”数据。

来源：jkavalik - #mysql freenode IRC

谢谢，贾斯汀

MYSQL查询每次运行时检索相同的结果

3 个答案: