sql 查询与 Row_Number 不同

Question

我正在与 sql 中的 distinct 关键字作斗争。 我只想在一列中显示唯一 (distinct) 值的所有行号，所以我尝试了：

SELECT DISTINCT id, ROW_NUMBER() OVER (ORDER BY id) AS RowNum
FROM table
WHERE fid = 64

但是下面的代码给了我distinct 值：

SELECT distinct id FROM table WHERE fid = 64

但是当用Row_Number尝试它时。
那么它就不起作用了。

Answer 1

试试这个

SELECT distinct id
FROM  (SELECT id, ROW_NUMBER() OVER (ORDER BY  id) AS RowNum
      FROM table
      WHERE fid = 64) t

或者使用RANK()代替行号并选择记录DISTINCT rank

SELECT id
FROM  (SELECT id, ROW_NUMBER() OVER (PARTITION BY  id ORDER BY  id) AS RowNum
      FROM table
      WHERE fid = 64) t
WHERE t.RowNum=1

这也返回不同的 ids

Answer 2

使用这个：

SELECT *, ROW_NUMBER() OVER (ORDER BY id) AS RowNum FROM
    (SELECT DISTINCT id FROM table WHERE fid = 64) Base

并将查询的“输出”作为另一个查询的“输入”。

使用 CTE：

; WITH Base AS (
    SELECT DISTINCT id FROM table WHERE fid = 64
)

SELECT *, ROW_NUMBER() OVER (ORDER BY id) AS RowNum FROM Base

这两个查询应该是等价的。

技术上你可以

SELECT DISTINCT id, ROW_NUMBER() OVER (PARTITION BY id ORDER BY id) AS RowNum 
    FROM table
    WHERE fid = 64

但是如果你增加DISTINCT字段的数量，你必须把所有这些字段都放在PARTITION BY中，例如

SELECT DISTINCT id, description,
    ROW_NUMBER() OVER (PARTITION BY id, description ORDER BY id) AS RowNum 
    FROM table
    WHERE fid = 64

我什至希望你理解你在这里违反了标准命名约定，id 可能应该是一个主键，根据定义是唯一的，所以 DISTINCT 将毫无用处，除非你将查询与一些JOINs/UNION ALL...

Answer 3

试试这个：

;WITH CTE AS (
               SELECT DISTINCT id FROM table WHERE fid = 64
             )
SELECT id, ROW_NUMBER() OVER (ORDER BY  id) AS RowNum
  FROM cte
 WHERE fid = 64

Answer 4

怎么样

;WITH DistinctVals AS (
        SELECT  distinct id 
        FROM    table 
        where   fid = 64
    )
SELECT  id,
        ROW_NUMBER() OVER (ORDER BY  id) AS RowNum
FROM    DistinctVals

SQL Fiddle DEMO

你也可以试试

SELECT distinct id, DENSE_RANK() OVER (ORDER BY  id) AS RowNum
FROM @mytable
where fid = 64

SQL Fiddle DEMO

Answer 5

这可以很简单，你已经很接近了

SELECT distinct id, DENSE_RANK() OVER (ORDER BY  id) AS RowNum
FROM table
WHERE fid = 64

Answer 6

This article covers an interesting relationship between ROW_NUMBER() and DENSE_RANK()（RANK() 函数没有特别处理）。当您需要在SELECT DISTINCT 语句上生成ROW_NUMBER() 时，ROW_NUMBER() will produce distinct values before they are removed by the DISTINCT keyword。例如。这个查询

SELECT DISTINCT
  v, 
  ROW_NUMBER() OVER (ORDER BY v) row_number
FROM t
ORDER BY v, row_number

...可能会产生这个结果（DISTINCT 无效）：

+---+------------+
| V | ROW_NUMBER |
+---+------------+
| a |          1 |
| a |          2 |
| a |          3 |
| b |          4 |
| c |          5 |
| c |          6 |
| d |          7 |
| e |          8 |
+---+------------+

而这个查询：

SELECT DISTINCT
  v, 
  DENSE_RANK() OVER (ORDER BY v) row_number
FROM t
ORDER BY v, row_number

...在这种情况下产生你可能想要的东西：

+---+------------+
| V | ROW_NUMBER |
+---+------------+
| a |          1 |
| b |          2 |
| c |          3 |
| d |          4 |
| e |          5 |
+---+------------+

请注意，DENSE_RANK() 函数的 ORDER BY 子句将需要 SELECT DISTINCT 子句中的所有其他列才能正常工作。

比较所有三个函数

使用 PostgreSQL / Sybase / SQL 标准语法（WINDOW 子句）：

SELECT
  v,
  ROW_NUMBER() OVER (window) row_number,
  RANK()       OVER (window) rank,
  DENSE_RANK() OVER (window) dense_rank
FROM t
WINDOW window AS (ORDER BY v)
ORDER BY v

...你会得到：

+---+------------+------+------------+
| V | ROW_NUMBER | RANK | DENSE_RANK |
+---+------------+------+------------+
| a |          1 |    1 |          1 |
| a |          2 |    1 |          1 |
| a |          3 |    1 |          1 |
| b |          4 |    4 |          2 |
| c |          5 |    5 |          3 |
| c |          6 |    5 |          3 |
| d |          7 |    7 |          4 |
| e |          8 |    8 |          5 |
+---+------------+------+------------+

Answer 7

使用DISTINCT 会在您添加字段时导致问题，并且它还可以掩盖您选择中的问题。像这样使用GROUP BY 作为替代方案：

SELECT id
      ,ROW_NUMBER() OVER (ORDER BY  id) AS RowNum
  FROM table
 where fid = 64
 group by id

然后您可以像这样从您的选择中添加其他有趣的信息：

,count(*) as thecount

或

,max(description) as description

Answer 8

问题太老了，我的回答可能不会增加太多，但这是我的两分钱，可以让查询有点用处：

;WITH DistinctRecords AS (
    SELECT  DISTINCT [col1,col2,col3,..] 
    FROM    tableName 
    where   [my condition]
), 
serialize AS (
   SELECT
    ROW_NUMBER() OVER (PARTITION BY [colNameAsNeeded] ORDER BY  [colNameNeeded]) AS Sr,*
    FROM    DistinctRecords 
)
SELECT * FROM serialize 

使用两个 cte 的用处在于，现在您可以在查询中更轻松地使用序列化记录，并且非常轻松地执行 count(*) 等。

DistinctRecords 将选择所有不同的记录，serialize 将序列号应用于不同的记录。之后，您可以将最终的序列化结果用于您的目的，而不会造成混乱。

Partition By 在大多数情况下可能不需要