retrieve the last inserted row from each user in d

问题:

I want to make a query in mysql with php and get the last inserted row from each user i have in a database. Let me give you an example.

Suppose we have a table with 10 rows

ID    Message   User     Date inserted

1      lala1    chris     13/02/2010 12:13
2      lala2    john      14/02/2010 12:14
3      lala3   george    15/03/2009 12:00
4      lala4    jack      01/04/2013 11:09
5      lala5    ina       12/08/2012 15:00
6      lala6    chris     13/03/2010 12:13
7      lala7    john      14/01/2010 12:04
8      lala8   george    15/02/2009 12:00
9      lala9    jack      01/03/2013 11:09
10     lala10    ina       12/05/2012 15:00

I want to make a query to get the last inserted rows from chris,john and ina ordered by date. So the result should be this:

5      lala5    ina       12/08/2012 15:00
6      lala6    chris     13/03/2010 12:13
2      lala2    john      14/02/2010 12:14

then after i get the last inserted rows from these users i want to make another query to get the previous last inserted rows for these users again so the result should be:

10     lala10    ina       12/05/2012 15:00
1      lala1    chris     13/02/2010 12:13
7      lala7    john      14/01/2010 12:04

and so on...

Any help appreciated!

回答1:

If you need to get the last, and then the previous last, and so on, you need to use a ranking function:

SELECT *
FROM (
  SELECT
    Users.*,
    CASE WHEN @lst=User THEN @row:=@row+1 ELSE @row:=0 END row,
    @lst:=User
  FROM
    Users
  WHERE
    User IN ('ina','chris','john')
  ORDER BY
    User, Date_ins DESC
) s
WHERE
  row=0

row=0 will get the last date, row=1 the previous last, and so on...

Please see fiddle here.

回答2:

For first part: (will give you all last insert record for all users. You can apply filter to get only 3 users)

SELECT t1.*
FROM Users t1
INNER JOIN (
    SELECT User, MAX(Date_Inserted) as MaxDate
    FROM Users
    GROUP BY User
) t2 ON t1.User = t2.User AND t1.Date_Inserted = t2.MaxDate

you could also try replacing

GROUP By User

with

WHERE User IN (User_1, User_2, User_3)

Replace User_1, User_2 and User_3 with those 3 user names

回答3:

Please take a look at strtotime found here. With it, you can convert time stamps to an integer and compare them. Also a better method would just be sorting the table by ID and limiting one.

回答4:

You must use GROUP BY in your SQL query

SELECT DISTINCT User, MAX(Date_inserted) FROM yourTable GROUP BY User