当我在查询中进行求和和左连接时,结果不再正确。这是因为在一张表中我加入的id比较常见,如何防止总和出错?
我有一个名为Norm
的表格
ID: 1 LocationID: 1 Norm: 0,22
ID: 1 LocationID: 1 Norm: 0,25
我有一个名为Hour
的表格
ID: 1 LocationID: 1
ID: 2 LocationID: 1
ID: 3 LocationID: 1
查询:
SELECT N.LocationID, SUM(N.Norm) FROM Norm N
结果:
LocationID: 1 Sum(N.Norm): 0,47
查询:
SELECT N.LocationID, SUM(N.Norm) FROM Norm N LEFT JOIN Hour H ON
N.LocationID = H.LocationID
结果:
LocationID: 1 Sum(N.Norm): 1,41
脚本:
CREATE TABLE Norm` ( `ID` INT NOT NULL , `LocationID` INTNOT NULL ,
`Norm` DECIMAL(10,2) NOTNULL );
INSERT INTO `Norm`(`ID`, `LocationID`, `Norm`)
VALUES (1,1, 0.22);
INSERT INTO `Norm`(`ID`, `LocationID`, `Norm`)
VALUES (2,1, 0.25)
CREATE TABLE `Hour` ( `ID` INT NOT NULL , `LocationID` INTNOT NULL );
INSERT INTO `Hour`(`ID`, `LocationID`) VALUES (1, 1);
INSERT INTO `Hour`(`ID`, `LocationID`) VALUES (2, 1);
INSERT INTO `Hour`(`ID`, `LocationID`) VALUES (3, 1);
我需要连接,但希望总和正确,如第一个,我该怎么做?
最佳答案
你可以试试这个
SELECT N.LocationID
, SUM(N.Norm)
FROM Norm N
LEFT JOIN (SELECT distinct locationid FROM Hour ) AS H
ON N.LocationID = H.LocationID
GROUP BY N.LocationID
关于mysql - 连接创建错误的结果查询,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/52293090/