通过获取匹配的 Id 来简化 TSQL，如果不匹配，则在行号中排在第一位答案

【问题标题】：Simplify TSQL by Getting Ids that matched or first in the row number if not matched通过获取匹配的 Id 来简化 TSQL，如果不匹配，则在行号中排在第一位
【发布时间】：2021-12-02 12:36:58
【问题描述】：

我有这个示例，其中 Id1 作为组，Id2 是组中唯一的 Id。

如果Id2和Id1一样，我想把它的行作为整个组的代表。

如果没有与Id2匹配的Id1，那么我想根据Id2的升序获取第一行。

我就是这样做的，但我只是想知道如何简化 tsql：

WITH cte AS
(
    SELECT 'A' AS Id1, '1' AS Id2, 'DSFSF' AS _detail
    UNION ALL
    SELECT 'A' AS Id1, '2' AS Id2, 'ASDF' AS _detail
    UNION ALL
    SELECT 'A' AS Id1, 'A' AS Id2, '434242' AS _detail
    UNION ALL
    SELECT 'B' AS Id1, '1' AS Id2, 'gsreew' AS _detail
    UNION ALL
    SELECT 'B' AS Id1, '2' AS Id2, 'werw' AS _detail
    UNION ALL
    SELECT 'B' AS Id1, '3' AS Id2, '67575' AS _detail
),
cte2 AS
(
    SELECT 
        *, 
        ROW_NUMBER() OVER (PARTITION BY Id1 ORDER BY Id2) AS rn,
        CASE 
            WHEN Id1 = Id2 THEN 1 ELSE 0 
        END AS _matchedid
    FROM
        cte
),
cte3 AS
(
    SELECT
        Id1, SUM(_matchedid) AS _matched
    FROM
        cte2
    GROUP BY
        Id1
)
SELECT *
FROM cte2 a
INNER JOIN cte3 b ON a.Id1 = b.Id1
WHERE b._matched = 1 AND a.Id1 = a.Id2

UNION ALL

SELECT *
FROM cte2 a
INNER JOIN cte3 b ON a.Id1 = b.Id1
WHERE b._matched = 0 AND a.rn = 1

【问题讨论】：

标签： sql-server tsql

【解决方案1】：

您可以为此使用条件行编号解决方案

WITH cte AS
(
    SELECT 'A' AS Id1, '1' AS Id2, 'DSFSF' AS _detail
    UNION ALL
    SELECT 'A' AS Id1, '2' AS Id2, 'ASDF' AS _detail
    UNION ALL
    SELECT 'A' AS Id1, 'A' AS Id2, '434242' AS _detail
    UNION ALL
    SELECT 'B' AS Id1, '1' AS Id2, 'gsreew' AS _detail
    UNION ALL
    SELECT 'B' AS Id1, '2' AS Id2, 'werw' AS _detail
    UNION ALL
    SELECT 'B' AS Id1, '3' AS Id2, '67575' AS _detail
),
cteWithRn AS
(
    SELECT *
      ROW_NUMBER() OVER (PARTITION BY Id1, CASE WHEN Id1 = Id2 THEN 0 ELSE 1 END, Id2) AS rn
    FROM cte
)
SELECT *
FROM cteWithRn
WHERE rn = 1;

【讨论】：

【解决方案2】：

一个想法使用TOP (1) WITH TIES 和ROW_NUMBER 与条件ORDER BY：

SELECT TOP (1) WITH TIES *
FROM CTE
ORDER BY ROW_NUMBER() OVER (PARTITION BY ID1 ORDER BY CASE ID1 WHEN ID2 THEN NULL ELSE ID2 END);

请注意，由于您的列ID2 是varchar，因此'10' 之类的值将比'2' 之类的值低。

【讨论】：