Question

我有一个SELECT语句，其LEFT OUTTER JOIN会导致表连接到自身。我遇到的问题是，当连接的右侧没有结果时，整个查询不会重新调整结果。我认为这是由于我的WHERE条款，但我尝试将COALESCE与NULL一起用作第二个值，但没有得到任何结果。

这是我的SQL查询：

SELECT  tch1.WeekEndingDate AS WeekEndingDate, 
        tch1.TotalHoursWorked AS TotalHoursWorked, 
        e.ID AS ID, 
        e.FirstName AS FirstName, 
        e.PTORemaining AS PTORemaining, 
        so1.Name AS Name, 
        Extent5.Name AS Name1, 
        e.FirstName + N' ' + e.LastName AS C1, 
        tch2.WeekEndingDate AS WeekEndingDate1, 
        tch2.TotalHoursWorked AS TotalHoursWorked1
FROM dbo.TimeCardHeader AS tch1
INNER JOIN dbo.Employee AS e ON tch1.EmployeeID = e.ID
INNER JOIN dbo.StatusOption AS so1 ON tch1.CurrentStatusID = so1.ID
LEFT OUTER JOIN dbo.TimeCardHeader AS tch2 ON tch1.EmployeeID = tch2.EmployeeID
INNER JOIN dbo.StatusOption AS Extent5 ON tch2.CurrentStatusID = Extent5.ID
WHERE (tch1.WeekEndingDate = '9/24/2016' AND tch2.WeekEndingDate = '10/1/2016' AND e.ID = 80)
OR (tch1.WeekEndingDate = '9/24/2016' AND tch2.WeekEndingDate = '10/1/2016' AND e.ManagerID = 80);

对于每个WeekEndingDate，我尝试使用WeekEndingDate = COALESCE('9/24/2016', NULL)

正在使用COALESCE正确的事情，我只是错误地使用它，或者我应该在这里使用另一种方法，以便即使没有TimeCardHeader，其WeekEndingDate为“10/1 / 2016＆＃39;我可以得到结果。

Answer 1

从我所看到的，您对StatusOption的内部联接基于来自TimeCardHolder（tch2）的CurrentStatusID，这是一个左连接。如果tch2中没有行，则内部联接将以您遇到的结果结束。有没有办法让StatusOption连接（Extent5）成为一个左连接，并将你的where与你已经尝试过的coalesce / isnull结合起来？

Answer 2

//captured the form data in variable $user= mysql_real_escape_string($_POST['user']); $message= mysql_real_escape_string($_POST['message']); $sql = "INSERT INTO testmessage2 (user, message) VALUES('$user','$message')";不会解决这个问题。现在你的WHERE语句可以被重写而不需要改变：

COALESCE()

哪个更容易理解。要引入WHERE tch1.WeekEndingDate = '9/24/2016' AND tch2.WeekEndingDate = '10/1/2016' AND (e.ID = 80 OR e.ManagerID = 80)为tch2.WeekEndingDate或NULL的记录，您只需在此简化版本中添加：

10/1/2016

也可以写成：

 WHERE tch1.WeekEndingDate = '9/24/2016' AND (tch2.WeekEndingDate = '10/1/2016' OR tch2.WeekEndingDate IS NULL) AND (e.ID = 80 OR e.ManagerID = 80)

此外，如注释中提到的@a_horse_with_no_name，您可以将WHERE子句设置为：在哪里tch1.WeekEndingDate ='9/24/2016'AND（e.ID = 80或e.ManagerID = 80）

将LEFT OUTER JOIN的ON更改为：

 WHERE tch1.WeekEndingDate = '9/24/2016' AND tch2.WeekEndingDate IN ('10/1/2016',NULL) AND (e.ID = 80 OR e.ManagerID = 80)

这将删除tch2之前的所有记录，但没有LEFT OUTER JOIN dbo.TimeCardHeader AS tch2 ON tch1.EmployeeID = tch2.EmployeeID AND tch2.WeekEndingDate = '10/01/2016'的{{1}}

Answer 3

将与tch2相关的谓词移动到join子句中： -

SELECT  tch1.WeekEndingDate AS WeekEndingDate, 
        tch1.TotalHoursWorked AS TotalHoursWorked, 
        e.ID AS ID, 
        e.FirstName AS FirstName, 
        e.PTORemaining AS PTORemaining, 
        so1.Name AS Name, 
        Extent5.Name AS Name1, 
        e.FirstName + N' ' + e.LastName AS C1, 
        tch2.WeekEndingDate AS WeekEndingDate1, 
        tch2.TotalHoursWorked AS TotalHoursWorked1
FROM dbo.TimeCardHeader AS tch1
INNER JOIN dbo.Employee AS e ON tch1.EmployeeID = e.ID
INNER JOIN dbo.StatusOption AS so1 ON tch1.CurrentStatusID = so1.ID
LEFT OUTER JOIN dbo.TimeCardHeader AS tch2 ON tch1.EmployeeID = tch2.EmployeeID 

    AND tch2.WeekEndingDate = '10/1/2016'

INNER JOIN dbo.StatusOption AS Extent5 ON tch2.CurrentStatusID = Extent5.ID
WHERE (tch1.WeekEndingDate = '9/24/2016'  AND e.ID = 80)
OR (tch1.WeekEndingDate = '9/24/2016' AND e.ManagerID = 80);

如果你在where子句中有它们，那么你将完全过滤掉连接的行。

当第二个表没有值时，LEFT OUTER JOIN不返回结果

3 个答案: