基于SQL Server条件的多行串联

Question

考虑一个包含如下数据的表，

COL1|   COL2|   active_flag
----|   ----|   ------------
1   |   A   |   Y
1   |   B   |   Y
1   |   C   |   Y
1   |   D   |   N
1   |   E   |   N
2   |   M   |   Y
2   |   N   |   Y
2   |   O   |   N
2   |   P   |   Y
2   |   Q   |   Y

我需要如下输出。

COL1|   COL2
----|   -----
1   |   ABC
1   |   D
1   |   E
2   |   MN
2   |   O
2   |   PQ

如何在SQL Server 2012

Answer 1

首先，您应该将列添加到id以获得稳定的排序。 然后，您可以计算每个组，然后使用FOR XML进行连接：

WITH cte AS(
    SELECT *, 
       CASE WHEN 
         LAG(active_flag) OVER(ORDER BY id)  <> active_flag
         OR LAG(active_flag) OVER(ORDER BY id) = 'N' AND active_flag = 'N' THEN 1
         ELSE 0
     b  END as l
    FROM t
), cte2 AS (
    SELECT *, SUM(l) OVER(ORDER BY id) AS grp
    FROM cte
)
SELECT DISTINCT col1, (SELECT '' + col2
              FROM cte2
              WHERE grp = c.grp
              ORDER BY id
              FOR XML PATH(''), TYPE
              ).value('.', 'NVARCHAR(MAX)') AS col2
FROM cte2 c;

Rextester演示

输出：

警告！

ORDER BY 1/0或ORDER BY (SELECT 1)不提供稳定的排序。