sql用于查找组中的最近记录

sql用于查找组中的最近记录

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问题描述

我有这样的表

  table_id | series_id | revision_id | year 
------------------------------------------
1 | 1 | 1 | 2010
2 | 2 | 1 | 2009
3 | 2 | 2 | 2008
4 | 2 | 2 | 2009
5 | 2 | 3 | 2010
6 | 2 | 3 | 2008
7 | 3 | 2 | 2007
8 | 3 | 3 | 2010
9 | 3 | 3 | 2010

当series = X时,我需要查找按revision_id分组时的max
in postgresql。



例如:当x = 2时,我期望这个结果

  table_id | series_id | revision_id | year 
------------------------------------------
2 | 2 | 1 | 2009
4 | 2 | 2 | 2009
5 | 2 | 3 | 2010

这不起作用

  SELECT * from table 
WHERE series_id = 2
和table_id IN(
SELECT table_id
FROM table
WHERE series_id = 2
GROUP by revision
ORDER BY年DESC

因为我需要返回一个字段,我没有按

分组

这里有一些类似的问题在其他SQL风格。



MySQL



SQL SERVER

$ b

  SELECT table_id,series_id, revision_id,year 
FROM tableName t INNER JOIN
(SELECT revision_id,max(year)AS year
FROM tableName
WHERE series_id = 2
GROUP BY revision_id)s
USING(revision_id,year)
WHERE series_id = 2;

结果:

 code> table_id | series_id | revision_id |年
---------- + ----------- + ------------- + ------
2 | 2 | 1 | 2009
4 | 2 | 2 | 2009
5 | 2 | 3 | 2010
(3 rows)


i have a table like such

table_id | series_id | revision_id | year
------------------------------------------
1        | 1         | 1           | 2010
2        | 2         | 1           | 2009
3        | 2         | 2           | 2008
4        | 2         | 2           | 2009
5        | 2         | 3           | 2010
6        | 2         | 3           | 2008
7        | 3         | 2           | 2007
8        | 3         | 3           | 2010
9        | 3         | 3           | 2010

I need to find the table_id for the max(year) when grouped by revision_id when series = Xin postgresql.

eg : when x =2 i expect this result

table_id | series_id | revision_id | year
------------------------------------------
2        | 2         | 1           | 2009
4        | 2         | 2           | 2009
5        | 2         | 3           | 2010

this doesn't work

SELECT * from table
WHERE series_id = 2
AND table_id IN (
    SELECT table_id
    FROM table
    WHERE series_id = 2
    GROUP by revision
    ORDER BY year DESC
)

I cannot figure out a way to do this in postgresql since I need to return a field i am not grouping by

here are some similar problems in other SQL flavors.

MySQLSQL Query, Selecting 5 most recent in each group

SQL SERVERSQL Server - How to select the most recent record per user?

解决方案

Query:

SELECT table_id, series_id, revision_id, year
FROM tableName t INNER JOIN
    (SELECT revision_id, max(year) AS year
    FROM tableName
    WHERE series_id = 2
    GROUP BY revision_id) s
USING (revision_id, year)
WHERE series_id = 2;

Result:

 table_id | series_id | revision_id | year
----------+-----------+-------------+------
        2 |         2 |           1 | 2009
        4 |         2 |           2 | 2009
        5 |         2 |           3 | 2010
(3 rows)

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08-14 23:29