比較兩個不同列中同一字段的值

Question

我需要在一個表中並列放置兩部分，它們具有相同的描述和不同的“外部ID”。 輸入表如下所示：

+--+-------+-----------+
|ID|OUTERID|DESCRIPTION|
+--+-------+-----------+
|1 |1      |some desc 1|
+--+-------+-----------+
|2 |1      |some desc 2|
+--+-------+-----------+
|3 |1      |some desc 3|
+--+-------+-----------+
|4 |2      |some desc 2|
+--+-------+-----------+
|5 |2      |some desc 3|
+--+-------+-----------+

這是我要從選擇中實現的目標：

+-------------+-------------+
|DESCRIPTION_1|DESCRIPTION_2|
+-------------+-------------+
|some desc 1  |NULL         |
+-------------+-------------+
|some desc 2  |some desc 2  |
+-------------+-------------+
|some desc 3  |some desc 3  |
+-------------+-------------+

我嘗試了一個簡單的JOIN，但是如您所見，我還需要顯示不匹配的值。

SELECT a.DESCRIPTION AS DESCRIPTION_1,
       b.DESCRIPTION AS DESCRIPTION_2
  FROM My_Table a
  JOIN My_Table b on a.DESCRIPTION = b.DESCRIPTION
WHERE a.OUTERID = 1
  AND b.OUTERID = 2

Answer 1

您需要dense_rank()並進行條件聚合：

select max(case when OUTERID = 1 then DESCRIPTION  end) as DESCRIPTION_1,
       max(case when OUTERID = 2 then DESCRIPTION  end) as DESCRIPTION_2
from (select t.*,
             dense_rank() over (order by DESCRIPTION) as seq
      from table t
     ) t
group by seq;

Answer 2

如果我理解正確，則可以使用完全外部聯接來執行此操作：

SELECT a.DESCRIPTION AS DESCRIPTION_1,
       b.DESCRIPTION AS DESCRIPTION_2
FROM (SELECT a.*
      FROM My_Table a
      WHERE a.OUTERID = 1
     ) a FULL JOIN
     (SELECT b.*
      FROM My_Table b 
      WHERE b.OUTERID = 2
     ) b
     ON a.DESCRIPTION = b.DESCRIPTION;

Answer 3

使用cte ：（不過，我不確定為什么您需要同時顯示兩列而不是僅標識“重復項”）

表：

Create Table #tbl
(
ID Int,
OUTERID Int,
DESCRIPTION VarChar(20)
)
Insert Into #tbl Values
(1,1,'some desc 1'),
(2,1,'some desc 2'),
(3,1,'some desc 3'),
(4,2,'some desc 2'),
(5,2,'some desc 3')

CTE

With cte As
(
Select Description, Count(Distinct OuterID) As recs From #tbl
Group By Description
)
Select 
      Case When recs = 2 Or recs = 1 Then Description End As Description_1, 
      Case When recs = 2 Then Description End As Description_2
From cte