Question

我只想返回第一个条件不存在的行然后从同一表返回新条件，以及其他条件：基本上...：

SELECT *   
FROM Table1     
WHERE

Condition#1: Column1=Column2

Condition#2: AND IF Column1 = Column2 doesn't exist (matching values for same ID) 
             THEN return results where Column3 = Column4

谢谢。

Answer 1

我怀疑这可以满足OP的需求，但是逻辑似乎很奇怪...

SELECT {Columns}
FROM YourTable YT
WHERE YT.Column1 = YT.Column2
   OR (YT.Column3 = YT.Column4
  AND  NOT EXISTS(SELECT 1
                  FROM YourTable e
                  WHERE YT.id = e.id
                    AND e.Column1 = e.Column2));

不过，不确定此处的性能如何，因为您可能最终使用该NOT EXISTS进行了表扫描。

Answer 2

根据评论，这是一种方法。

SELECT *    
FROM Table1      
WHERE Column1 = Column2 
UNION 
SELECT * 
FROM Table2 
WHERE  Column1 != Column2 and Column3 = Column4

Answer 3

您可以使用简单的布尔值来做到这一点：

WHERE
Column1 = Column2
OR
Column3 = Column4

维恩图：

将返回所有阴影区域，包括当Column1 = Column2和Column3 = Column4（深色阴影交叉点）时

如果您不希望同时满足这两个条件的行，则可以修改逻辑：

WHERE
Column1 = Column2
OR
(Column1 <> Column2 
AND
Column3 = Column4)

除了交叉点为白色且不包括交点之外，维恩看起来都一样。

Answer 4

首先，您需要检查您的情况。因此，您可以计算表中有多少C1 = C2

SELECT [id], COUNT(CASE WHEN C1 = C2 THEN 1 END) as c1_c2
FROM Table1
GROUP BY [id]

那你有两个条件

首先，当您有c1 = c2时

  (c1 = c2 and c1_c2 > 0 )

当没有c1 = c2时是第二个

  (c1_c2 = 0 and c3 = c4)

SQL DEMO: ：因为是OR，而c1_c2的计数决定了该位置的哪一侧工作。

WITH c12 as (
    SELECT [id], COUNT(CASE WHEN C1 = C2 THEN 1 END) as c1_c2_cnt
    FROM Table1
    GROUP BY [id]
) 
SELECT *
FROM Table1 T
JOIN c12 C
  ON T.[id] = C.[id]  
WHERE  ( C.c1_c2_cnt > 0 and T.c1 = T.c2 )
   OR  ( C.c1_c2_cnt = 0 and T.c3 = T.c4 )

输出

Answer 5

另一种方法：

DECLARE 
    @t TABLE( ID INT, col1 CHAR(1), col2 CHAR(1), col3 INT, col4 INT)

INSERT INTO @t VALUES 
(1234,'A','B',100,100),
(1234,'A','A',100,100),
(2468,'A','C',125,125),
(2468,'A','B',100,150)

SELECT 
    ID
,   col1
,   col2
,   col3
,   col4
FROM (
    SELECT *, ROW_NUMBER() OVER(PARTITION BY ID, col1 ORDER BY col2) RN
    FROM (
        SELECT *
        FROM @t
        WHERE 
            col3 = col4
        AND col1 = col2
        UNION ALL 
        SELECT *
        FROM @t
        WHERE 
            col3 = col4
        AND ID NOT IN(
            SELECT ID
            FROM @t
            WHERE 
                col3 = col4
            AND col1 = col2
            )
    ) D
) E
WHERE 
    RN = 1

在Where子句SQL Server

5 个答案: