我的数据不会显示，除非两个表之间匹配

Question

我的问题是，只有MainRule表的ID与Table1表匹配时，此查询才有效。即使MainRule表没有匹配的ID，我也需要查询才能工作。即使MainRule表中没有匹配的记录，Table1中的记录也应该显示。

这里是我的代码：

SELECT Person, OrderNum, Name, County, SubmitDate, Days1, 
     SUM(Date_Diff) - 1 AS [Number of Uncleared Days] 
    From 
    (SELECT D1.RecordID AS Person, D3.[case no] AS OrderNum, 
      D3.FullName AS Name, D3.County, D3.[SignedDate] AS SubmitDate, 
        DATEDIFF(d, D3.[SignedDate], D3.closedate) AS Days1, 
        DATEDIFF(DAY, [HoldDate], 
        (SELECT TOP 1 [StatusDate] 
        FROM [MainRule] D2 
        WHERE D2.Status = 'Cleared' 
         AND D1.RecordID = D2.RecordID 
         AND D1.StatusDate < D2.StatusDate)) AS [Date_Diff] 
     FROM [MainRule] AS D1 INNER JOIN table1 AS D3 ON D3.ID = D1.RecordID 
     WHERE D1.Status = 'UnCleared') SubQ 
WHERE (SubmitDate BETWEEN '10/01/2017' and '10/17/2017') 
GROUP BY Person, OrderNum, Name, County, SubmitDate, Days1 

Answer 1

你有两个问题：INNER JOIN（由对方的回答解释），以及WHERE D1.Status = 'UnCleared'。

不管你的连接是什么，WHERE子句将排除没有匹配的MainRule行的行。

尝试类似WHERE D1.Status = 'UnCleared' OR D1.Status IS NULL。

Answer 2

只需使用LEFT JOIN代替：

SELECT Person, OrderNum, Name, County, SubmitDate, Days1, 
     SUM(Date_Diff) - 1 AS [Number of Uncleared Days] 
    From 
    (SELECT D1.RecordID AS Person, D3.[case no] AS OrderNum, 
      D3.FullName AS Name, D3.County, D3.[SignedDate] AS SubmitDate, 
        DATEDIFF(d, D3.[SignedDate], D3.closedate) AS Days1, 
        DATEDIFF(DAY, [HoldDate],              
        (SELECT TOP 1 [StatusDate] 
        FROM [MainRule] D2 
        WHERE D2.Status = 'Cleared' 
         AND D1.RecordID = D2.RecordID 
         AND D1.StatusDate < D2.StatusDate)) AS [Date_Diff] 
     FROM table1 AS D3 
     LEFT JOIN [MainRule] AS D1 ON D3.ID = D1.RecordID 
     WHERE D1.Status = 'UnCleared') SubQ 
WHERE (SubmitDate BETWEEN '10/01/2017' and '10/17/2017') 
GROUP BY Person, OrderNum, Name, County, SubmitDate, Days1 

这样，您将得到MainRule（左表）中的所有行，即使没有匹配排在另一个表table1。

你应该阅读有关连接类型之间的区别：

• A Visual Explanation of SQL Joins