ROW_NUMBER对COUNT（1）？

Question

两种选择中的哪一种更好？

ROW_NUMBER() OVER (PARTITION BY...)

或

COUNT(1) OVER (PARTITION BY ...)

我找不到任何这样的问题。

修改

DBMS: SQL-SERVER (version >= 2008)


In my case the over partition is guaranteed by a single field:
ROW_NUMBER() OVER (PARTITION BY ELEMENT ORDER BY EMPLOYEE)
COUNT(1) OVER (PARTITION BY ELEMENT ORDER BY EMPLOYEE)


ELEMENT      EMPLOYEE       ROW_NUMBER       COUNT

0000001      00000003       1                1
0000001      00000004       2                2
0000001      00000005       3                3
0000003      00000045       1                1
0000003      00000046       2                2

Answer 1

当COUNT(1)列中的同一组值重复时，

ORDER BY的行为会有所不同。

以下是SQL Server的一个示例：

IF OBJECT_ID('tempdb..#Example') IS NOT NULL
    DROP TABLE #Example

CREATE TABLE #Example (
    Number INT,
    GroupNumber INT)

INSERT INTO #Example (
    Number,
    GroupNumber)
VALUES
    (NULL, 1),
    (100, 1),
    (101, 1),
    (102, 1),
    (103, 1),

    (NULL, 2),
    (NULL, 2),
    (NULL, 2),
    (200, 2),
    (201, 2),
    (202, 2),

    (300, 3),
    (301, 3),
    (301, 3),
    (301, 3),
    (302, 3)


SELECT
    E.*,
    RowNumber = ROW_NUMBER() OVER (PARTITION BY E.GroupNumber ORDER BY E.Number ASC),
    CountOver = COUNT(1) OVER (PARTITION BY E.GroupNumber ORDER BY E.Number ASC)
FROM
    #Example AS E

结果：

Number      GroupNumber RowNumber            CountOver
----------- ----------- -------------------- -----------
NULL        1           1                    1
100         1           2                    2
101         1           3                    3
102         1           4                    4
103         1           5                    5

NULL        2           1                    3 Here
NULL        2           2                    3
NULL        2           3                    3
200         2           4                    4
201         2           5                    5
202         2           6                    6

300         3           1                    1
301         3           2                    4 Here
301         3           3                    4
301         3           4                    4
302         3           5                    5

这是因为它是一个计数而不是行数。你应该使用适合你需要的那个。