Question

我在一个数据库表中有以下数据。

Name                LeftId    RightId
------------------------------------------
Cat                     1  
Cat                     1
Dog                     2
Dog                     2
Dog                               3
Dog                               3
Gerbil                  4         5 
Cat                
Bird
Cow                     6
Cow
Cow                               7
Dog                     8         9

请注意，对于LeftId和RightId，某些行没有数据。

现在，我想做的是找到两个不同的查询

在两个列中的一列中至少有1个Id的所有行和这两个Id列中没有数据的行。

例如

Cat     1
Cow     6 (or 7 .. i'm not worried)

LeftId和RightId为NULL的所有行按相同名称分组。如果另一行（具有相同名称）在LeftId或RightId中具有值，则不会返回此名称。

例如

Bird

HMM ..

编辑：正确地重新提出第一个问题。

Answer 1

对于第一个查询，您需要符合以下两个条件的行：

行中的Name出现在LeftId和RightId都为NULL的同一行的表格中。
行中的Name出现在同一行的表格中，LeftId和RightId中至少有一个不为空。

嗯，＃1由：

SELECT Name FROM Tbl WHERE (LeftId IS NULL) AND (RightId IS NULL)

＃2由：

SELECT Name FROM Tbl WHERE (LeftId IS NOT NULL) OR (RightId IS NOT NULL)

你可以相交，看看哪个Name出现在两个列表中：

SELECT Name FROM Tbl WHERE (LeftId IS NULL) AND (RightId IS NULL)
INTERSECT
SELECT Name FROM Tbl WHERE (LeftId IS NOT NULL) OR (RightId IS NOT NULL)

返回：

Name
----
Cat
Cow

但是你想要LeftId和RightId，而你不关心哪个，所以我想我们会在名称上聚合：

SELECT Name, MIN(LeftId) AS LeftId, MIN(RightId) AS RightId 
    FROM Tbl WHERE Tbl.Name IN (
      SELECT Name FROM Tbl WHERE (LeftId IS NULL) AND (RightId IS NULL)
      INTERSECT
      SELECT Name FROM Tbl WHERE (LeftId IS NOT NULL) OR (RightId IS NOT NULL)
    )
GROUP BY Name

返回

Name  LeftId  RightId
----  ------  -------
Cat   1
Cow   6       7

lc已建议使用COALESE将这两个ID转换为单个ID。那怎么样：

SELECT Name, COALESCE(MIN(LeftId),MIN(RightId)) AS Id 
    FROM Tbl WHERE Tbl.Name IN (
      SELECT Name FROM Tbl WHERE (LeftId IS NULL) AND (RightId IS NULL)
      INTERSECT
      SELECT Name FROM Tbl WHERE (LeftId IS NOT NULL) OR (RightId IS NOT NULL)
    )
GROUP BY Name

返回：

Name  Id
----  --
Cat   1
Cow   6

对于第二个查询，您需要符合以下条件的行：

Name仅出现在没有LeftId和RightId

我想不出在一组标准中在SQL中进行那种自引用查询的方法，所以我将其分解为两个标准。必须遵守两者才能被接受：

Name显示在没有LeftId和RightId
Name not 会出现在LeftId或RightId

做＃1只是：

SELECT Name FROM Tbl WHERE (LeftId IS NULL) AND (RightId IS NULL)

但＃2很棘手。当然，与＃2相反（“Name或LeftId行中出现的所有RightId都与之前相同：

SELECT Name FROM Tbl WHERE (LeftId IS NOT NULL) OR (RightId IS NOT NULL)

现在是棘手的一点 - 我们希望所有符合＃1的行但不遵守＃2的相反行。这是 EXCEPT 有用的地方：

SELECT Name FROM Tbl WHERE (LeftId IS NULL) AND (RightId IS NULL)
EXCEPT
SELECT Name FROM Tbl WHERE (LeftId IS NOT NULL) OR (RightId IS NOT NULL)

返回：

Name
----
Bird

这就是我们想要的！

Answer 2

如果我理解正确，那么这是相当微不足道的：

1：

SELECT * 
FROM your_table 
WHERE (LeftId IS NOT NULL 
AND RightId IS NULL)
OR
(LeftId IS NULL 
AND RightId IS NOT NULL)

2：

SELECT * 
FROM your_table
WHERE 
    NOT EXISTS 
              (SELECT * FROM your_table y1
               WHERE (y1.LeftId IS NOT NULL OR y1.RightId IS NOT NULL)
               AND y1.name = your_table.name)

如果这不对，那么也许你可以澄清一下。

修改：已更新

Answer 3

查询1）

SELECT * 
FROM Table 
WHERE (LeftID IS NULL AND RightID IS NOT NULL) 
    OR (LeftID IS NOT NULL AND RightID IS NULL)

查询2）

SELECT * 
FROM Table 
WHERE LeftID IS NULL AND RightID IS NULL

Answer 4

我希望我能在这里正确理解你。

查询1：

SELECT t1.Name, COALESCE(MIN(t1.LeftID), MIN(t1.RightID))
FROM Table t1
WHERE EXISTS(SELECT t2.Name
             FROM Table t2
             WHERE t2.Name = t1.Name 
             AND   t2.LeftID IS NULL AND t2.RightID IS NULL)
AND   COALESCE(MIN(t1.LeftID), MIN(t1.RightID)) IS NOT NULL
GROUP BY t1.Name

查询2：

SELECT t1.Name
FROM Table t1
WHERE NOT EXISTS(SELECT t2.Name
                 FROM Table t2
                 WHERE t2.Name = t1.Name
                 AND   (t2.LeftID IS NOT NULL OR t2.RightID IS NOT NULL))

Answer 5

查询1：

SELECT [Name], [LeftID], [RightID]

FROM [TestTable]

WHERE -- "All rows which have at least 1 Id in one of the two columns"
      ([LeftID] IS NOT NULL OR [RightID] IS NOT NULL)
      OR
      -- "Rows with NO data in both of those two Id columns"
      ([LeftID] IS NULL AND [RightID] IS NULL)

查询2：

SELECT [Name], [LeftID], [RightID]

FROM [TestTable]

WHERE -- "All the rows where LeftId and RightId are NULL
      -- grouped by the same name"
      ([LeftID] IS NULL AND [RightID] IS NULL)
      AND
      -- "If another row (with the same name) has a value
      -- in the LeftId or RightId, this name will not be returned"    
      ([Name] NOT IN (SELECT DISTINCT [Name] FROM [TestTable]
                      WHERE [LeftID] IS NOT NULL
                            OR
                            [RightID] IS NOT NULL))

GROUP BY [Name], [LeftID], [RightID]

结果：

Name                                               LeftID      RightID
-------------------------------------------------- ----------- -----------
Cat                                                1           NULL
Cat                                                1           NULL
Dog                                                2           NULL
Dog                                                2           NULL
Dog                                                NULL        3
Dog                                                NULL        3
Gerbil                                             4           5
Cat                                                NULL        NULL
Bird                                               NULL        NULL
Cow                                                6           NULL
Cow                                                NULL        NULL
Cow                                                NULL        7
Dog                                                8           9

(13 row(s) affected)

Name                                               LeftID      RightID
-------------------------------------------------- ----------- -----------
Bird                                               NULL        NULL

(1 row(s) affected)

如何清理这个Sql数据？

5 个答案: