MySQL extracts the first N records from each group.

The requirement is as follows (a problem on csdn): There is a table in MySQL: article (field: ID, type, date), type has 1-10, 10 types. Now we need to use SQL to find a collection of the First n data of the latest time in each type.

 

There should be many ways to implement this problem. Next we will talk about the implementation of a master we can see on the Internet (using an SQL statement, I personally feel very good, so I will share with you ):

 

Select A1. * from Article A1

Inner join

(Select a. type, A. date from Article A left join Article B

On a. type = B. Type and A. Date <= B. Date

Group by A. type, A. Date

Having count (B. Date) <= 2

) B1

On a1.type = b1.type and a1.date = b1.date

Order by a1.type, a1.date DESC

Note: 2 in the preceding SQL statement represents N as mentioned above.