Question

假设我有两个数据表：

Table A
ID    Colors
--    ------
1     Blue
1     Green
1     Red

Table B
ID    States
--    ------
1     MD
1     VA
1     WY
1     CA

是否可以加入这些表，以便获得以下内容而不是12行？

ID    Colors    States
--    ------    ------
1     Blue      MD
1     Green     VA
1     Red       WY
1               CA

颜色和状态列之间没有关联，列的顺序无关紧要。（例如，Blue可以位于MD，VA，WY或CA旁边）每个ID中每列（颜色或状态）中的项目数不相等。

感谢。

Answer 1

您可以使用row_number()创建假连接列来执行此操作：

select coalesce(a.id, b.id) as id, a.colors, b.states
from (select a.*, row_number() over (order by id) as seqnum
      from a
     ) a full outer join
     (select b.*, row_number() over (order by id) as seqnum
      from b
     ) b
     on b.seqnum = a.seqnum

实际上，在Oracle中，您也可以使用rownum：

select coalesce(a.id, b.id) as id, a.colors, b.states
from (select a.*, rownum as seqnum
      from a
     ) a full outer join
     (select b.*, rownum as seqnum
      from b
     ) b
     on b.seqnum = a.seqnum

Answer 2

您也可以使用CTE（公用表格式），如下所示：

WITH TableA (ID, Color) AS
(
    SELECT "ID", Color 
    FROM DatabaseName.TableA
)
, Joined AS (
    SELECT 
        a.ID AS "AID",
        a.Color
        b.ID AS "BID", 
        b."State"
    FROM, 
        TableA AS a
            RIGHT OUTER JOIN DatabaseName.TableB AS b ON a.ID = b.ID
)

SELECT
    AID,
    Color,
    State
FROM
    Joined

是否可以仅通过每个表中的第一个ID连接多个行的两个表？

2 个答案: