将多行合并为最少数量的不同值行

Question

在 SQL Server 中，是否有人知道将多行数据合并/展平为仅包含不同非空值的尽可能少的行的好方法。

IE

像这样的数据集：

像这样：

如果有帮助，之前的数据集是一个透视线列表，但没有聚合。我无法在枢轴期间聚合它，因为我想保留每个不同的值而不是采用 MAX 或 MIN。

我能想到的唯一方法是将数据拆分并将它们全部重新组合在一起，这不会非常有效。

Answer 1

您可以通过以下几种方法来完成任务结果集。

创建测试数据

CREATE TABLE #table (
    ID INT NOT NULL,
    Col1 VARCHAR(100) NULL,
    Col2 VARCHAR(100) NULL,
    Col3 VARCHAR(100) NULL,
    Col4 VARCHAR(100) NULL,
    Col5 VARCHAR(100) NULL
)
GO
INSERT INTO #table (ID, Col1, Col2, Col3, Col4, Col5)
VALUES  (37850, '1A', NULL, '3A', NULL, '5A'),
        (37850, NULL, NULL, '3B', NULL, NULL),
        (37850, NULL, '2A', '3C', '4A', '5B'),
        (37850, NULL, NULL, NULL, NULL, NULL),
        (37850, NULL, NULL, NULL, NULL, '5C'),
        (37850, NULL, '2B', NULL, NULL, NULL),
        (37850, NULL, NULL, NULL, NULL, '5D'),
        (37850, NULL, NULL, NULL, NULL, NULL),
        (37850, NULL, NULL, NULL, '4B', '5E'),
        (37850, NULL, NULL, NULL, '4C', NULL),
        (37850, NULL, NULL, NULL, '4D', NULL)
GO
CREATE CLUSTERED INDEX CI ON #table (ID)
GO

执行所需的合并和展平，对每列数据进行一次扫描，对最后一组行仅进行一次排序（或散列组）

SELECT ID,
        -- Pivot the data for each ID / row number pair,
        MIN(CASE WHEN colNumber = 1 THEN val END) AS Col1,
        MIN(CASE WHEN colNumber = 2 THEN val END) AS Col2,
        MIN(CASE WHEN colNumber = 3 THEN val END) AS Col3,
        MIN(CASE WHEN colNumber = 4 THEN val END) AS Col4,
        MIN(CASE WHEN colNumber = 5 THEN val END) AS Col5
FROM (
    -- Within each ID, assign an arbitrary row number to each non-NULL column value
    SELECT ID, ROW_NUMBER() OVER (PARTITION BY ID ORDER BY (SELECT 0) ASC) AS rowNum, 1 AS colNumber, Col1 AS val FROM #table WHERE Col1 IS NOT NULL UNION ALL
    SELECT ID, ROW_NUMBER() OVER (PARTITION BY ID ORDER BY (SELECT 0) ASC) AS rowNum, 2 AS colNumber, Col2 AS val FROM #table WHERE Col2 IS NOT NULL UNION ALL
    SELECT ID, ROW_NUMBER() OVER (PARTITION BY ID ORDER BY (SELECT 0) ASC) AS rowNum, 3 AS colNumber, Col3 AS val FROM #table WHERE Col3 IS NOT NULL UNION ALL
    SELECT ID, ROW_NUMBER() OVER (PARTITION BY ID ORDER BY (SELECT 0) ASC) AS rowNum, 4 AS colNumber, Col4 AS val FROM #table WHERE Col4 IS NOT NULL UNION ALL
    SELECT ID, ROW_NUMBER() OVER (PARTITION BY ID ORDER BY (SELECT 0) ASC) AS rowNum, 5 AS colNumber, Col5 AS val FROM #table WHERE Col5 IS NOT NULL
) x
GROUP BY ID, rowNum
GO

在 SQL Server 2017+ 中，通过对数据的单次扫描而不进行排序来执行所需的合并和展平

SELECT s.ID,
    -- Pivot the data for each ID / row number pair,
    MIN(CASE WHEN v.colNum = 1 THEN v.value END) AS Col1,
    MIN(CASE WHEN v.colNum = 2 THEN v.value END) AS Col2,
    MIN(CASE WHEN v.colNum = 3 THEN v.value END) AS Col3,
    MIN(CASE WHEN v.colNum = 4 THEN v.value END) AS Col4,
    MIN(CASE WHEN v.colNum = 5 THEN v.value END) AS Col5
FROM (
    -- For each ID, build the list of non-NULL values, using
    -- a delimiter that will not exist in your data
    SELECT t.ID,
        STRING_AGG(t.Col1,CHAR(0)) as stringAgg1,
        STRING_AGG(t.Col2,CHAR(0)) as stringAgg2,
        STRING_AGG(t.Col3,CHAR(0)) as stringAgg3,
        STRING_AGG(t.Col4,CHAR(0)) as stringAgg4,
        STRING_AGG(t.Col5,CHAR(0)) as stringAgg5
    FROM #table t
    GROUP BY t.ID
) s
OUTER APPLY (
    -- For each ID, unpivot the list of non-NULL values,
    -- appending an arbitrary row number to each value
    SELECT value, 1 AS colNum, ROW_NUMBER() OVER (ORDER BY (SELECT 0)) AS rn FROM STRING_SPLIT(s.stringAgg1,CHAR(0)) UNION ALL
    SELECT value, 2 AS colNum, ROW_NUMBER() OVER (ORDER BY (SELECT 0)) AS rn FROM STRING_SPLIT(s.stringAgg2,CHAR(0)) UNION ALL
    SELECT value, 3 AS colNum, ROW_NUMBER() OVER (ORDER BY (SELECT 0)) AS rn FROM STRING_SPLIT(s.stringAgg3,CHAR(0)) UNION ALL
    SELECT value, 4 AS colNum, ROW_NUMBER() OVER (ORDER BY (SELECT 0)) AS rn FROM STRING_SPLIT(s.stringAgg4,CHAR(0)) UNION ALL
    SELECT value, 5 AS colNum, ROW_NUMBER() OVER (ORDER BY (SELECT 0)) AS rn FROM STRING_SPLIT(s.stringAgg5,CHAR(0))
) v
-- For each ID, group together all column values with same row number
GROUP BY s.ID, v.rn
GO

可视化测试数据

可视化结果