Question

我希望有人可以提供帮助。我有一张桌子......

name    date    number
John    2014-01-01    5
Sally   2014-01-01    7
John    2013-12-24    2
Sally   2013-12-24    7
John    2013-11-10    1
Sally   2012-11-10    8

我想获得每个人的最新2（或x）记录，例如

John    2014-01-01    5
John    2013-12-24    2
Sally   2014-01-01    7
Sally   2013-12-24    7

我不知道从哪里开始。如果有人能够对此有所了解，我将非常感激。如果您能够为学习目的解释解决方案，那也很好（如果您有时间的话）！

非常感谢

朱

Answer 1

SELECT x.* 
  FROM my_table x 
  JOIN my_table y 
    ON y.name = x.name 
   AND y.date >= x.date 
 GROUP 
    BY x.name
     , x.date 
HAVING COUNT(*) <= 2 
 ORDER 
    BY name,date DESC;

Answer 2

Select Count(Distinct Names) "yourtable" 

Group By Names

计数结果你将乘以x和tis将是你下一个查询的限制意义：

Select Distinct Names,date,number from "yourtablename"

limit Count(Distinct Names)*X

order by Names

为组中的每个选择最后n个日期记录

2 个答案: