Question

对于此示例表：

表A：

Col1   Col2
-----------
2015   A
2015   B
2015   C

表B：

Col1    Col2
------------ 
2015    X
2015    Y
2015    Z

我希望查询返回：

Col1    Col2
------------
A       X
B       Y
C       Z

我尝试过这样的事情：

SELECT TA.COL2, TB.COL2
FROM
  (SELECT * FROM TABLE_A WHERE COL1=2015) TA,
  (SELECT * FROM TABLE_B WHERE COL1=2015) TB,

但是我得到重复的结果

Col1    Col2
-----------
A       X
A       Y
A       Z
B       X
B       Y
B       Z
C       X
C       Y
C       Z

Answer 1

一种方法是使用行号：

SELECT TA.COL2, TB.COL2
FROM
  (SELECT TABLE_A.COL2, ROWNUM AS R1 FROM TABLE_A WHERE COL1=2015) TA,
  (SELECT TABLE_B.COL2, ROWNUM AS R2 FROM TABLE_B WHERE COL1=2015) TB,
WHERE T1.R1 = T2.R2

Answer 2

在SELECT语句中，在SELECT子句之后包含DISTINCT或DISTINCTROW关键字。更多细节： http://www.geeksengine.com/database/basic-select/eliminate-duplicate-rows.php

Answer 3

不确定为什么要这样做，但这是我的方法。

SELECT
    TA.COL2 AS Col1,
    TB.COL2 AS Col2
FROM
    (SELECT COL1, COL2, ROW_NUMBER() OVER (PARTITION BY COL1 ORDER BY COL2) AS Seq FROM TABLE_A) TA
JOIN
    (SELECT COL1, COL2, ROW_NUMBER() OVER (PARTITION BY COL1 ORDER BY COL2) AS Seq FROM TABLE_B) TB
    ON TA.COL1 = TB.COL1
        AND TA.Seq = TB.Seq

Answer 4

您可能想要使用union all / group by方法：

SELECT MAX(COL2_a) as COL2_a, MAX(COL2_B) as COL2_B
FROM ((SELECT COL2 as COL2_A, NULL as COL2_B,
              ROW_NUMBER() OVER (ORDER BY COL2) as seqnum
       FROM TABLE_A
       WHERE COL1 = 2015
      ) UNION ALL
      (SELECT NULL, COL2, ROW_NUMBER() OVER (ORDER BY COL2) as seqnum
       FROM TABLE_B
       WHERE COL1 = 2015
      ) UNION ALL
     ) t
GROUP BY seqnum;

或者，使用FULL JOIN：

SELECT a.COL2 as COL2_a, b.COL2 as COL2_B
FROM (SELECT a.*,
             ROW_NUMBER() OVER (ORDER BY COL2) as seqnum
      FROM TABLE_A a
      WHERE COL1 = 2015
     ) a FULL JOIN
     (SELECT b.*,
             ROW_NUMBER() OVER (ORDER BY COL2) as seqnum
      FROM TABLE_B b
      WHERE COL1 = 2015
     ) b
     ON a.seqnum = b.seqnum;

如果一个表比另一个表具有更多的值，则这两种方法都将返回 all 个值。

从不同的表格中选择列而不重复行

4 个答案: