TSQL UNION 获取唯一值答案

【问题标题】：TSQL UNION GETTING UNIQUE VALUETSQL UNION 获取唯一值
【发布时间】：2012-09-16 04:03:30
【问题描述】：

我正在尝试根据两个标准获取两个数据库之间的唯一记录。标准是：

如果在数据库 1 中找到数据（在下面的示例中为 @SCCM），它被优先考虑
获取所选数据库中的 MAX 资源 ID

这是一个例子，它是一半的工作。数据库首选项有效，但该数据库内的最大资源 ID 无效。现在它正在选择@SMS 和@SCCM 之间的最大值


DECLARE @SMS TABLE (
    name0 varchar(100),
    resid int
)

DECLARE @SCCM TABLE (
    name0 varchar(100),
    resid int
)

INSERT INTO @SMS
SELECT 'TEST', 1000 UNION
SELECT 'TEST', 1500 UNION
SELECT 'TEST1', 2000 UNION
SELECT 'TEST2', 3000 UNION
SELECT 'TEST3', 4000

INSERT INTO @SCCM
SELECT 'TEST', 100 UNION
SELECT 'TEST', 150 UNION
SELECT 'TEST1', 200 UNION
SELECT 'TEST2', 300

SELECT MIN(SMSDB) as SMSDB, MAX(Resid), Name0 FROM
(
    SELECT name0, resid, 2 as SMSDB FROM @SMS
    UNION ALL
    SELECT name0, resid, 1 as SMSDB FROM @SCCM
) as tbl
GROUP BY NAME0

预期结果：

SMSDB | Resid | Name0
----------------------
1     | 150   | TEST
1     | 200   | TEST1
1     | 300   | TEST2
2     | 4000  | TEST3

【问题讨论】：

标签： sql-server tsql max min union-all

【解决方案1】：

你可以使用partitions:

;WITH tbl as
(
    SELECT name0, resid, 2 as SMSDB FROM SMS
    UNION ALL
    SELECT name0, resid, 1 as SMSDB FROM SCCM
),
t as (
    SELECT *, 
           ROW_NUMBER()  
           over (partition By name0 order by SMSDB, resid desc ) 
           as rn
    FROM tbl
)
SELECT * FROM t
WHERE rn = 1

Results:

| NAME0 | RESID | SMSDB | RN |
------------------------------
|  TEST |   150 |     1 |  1 |
| TEST1 |   200 |     1 |  1 |
| TEST2 |   300 |     1 |  1 |
| TEST3 |  4000 |     2 |  1

【讨论】：

【解决方案2】：

分区解决方案实际上可能更好，但它伤害了我的大脑。如果 SCCM 中存在 SMS 中的值，那么仅排除这些值怎么样？

SELECT MIN(SMSDB) as SMSDB, MAX(Resid), Name0 FROM
(
    SELECT name0, resid, 2 as SMSDB FROM @SMS SMS
    WHERE NOT EXISTS (SELECT * FROM @SCCM WHERE name0 = SMS.name0)
    UNION ALL
    SELECT name0, resid, 1 as SMSDB FROM @SCCM
) as tbl
GROUP BY NAME0

甚至

SELECT 1 as SMSDB, MAX(resid), name0  FROM @SCCM
GROUP BY name0
UNION ALL
SELECT 2 as SMSDB, MAX(resid), name0 FROM @SMS SMS
WHERE NOT EXISTS (SELECT * FROM @SCCM WHERE name0 = SMS.name0)
GROUP BY name0
ORDER BY name0

【讨论】：