How can i remove the oldest entries in my SQL result?

问题

I want to get only the last reports, for all items but only the most recent report for each item_id. Here is my current solution:

SELECT distinct * FROM t.reports ORDER BY created DESC LIMIT 100

My table consists of the following columns:

id | user | item_id |  created
'2', '1',   '2643',  '2017-06-13 16:28:34'
'3', '1',   '19333', '2017-06-13 19:26:56'
'4', '1',   '19333', '2017-06-13 19:29:24'
'5', '1',   '1319',  '2017-06-13 19:29:56'
'6', '1',   '1319',  '2017-06-13 19:30:16'
'7', '1',   '1319',  '2017-06-13 19:30:17'
'8', '1',   '1319',  '2017-06-13 19:30:18'
'9', '1',   '1319',  '2017-06-13 19:30:25'
'10','1',   '1319',  '2017-06-13 19:31:51'

I want no duplicate item_ids AND only the most recent entry for that item. BUT i also want ALL reports, but no duplicate item reports!

EXAMPLE: i expect that when i execute my query, i only get row 2,4 and 10 returned.

回答1:

Try this:

select a.id,a.user,a.item_id,a.created
from reports as a
where a.created=(select max(created) 
                from reports as b
                where a.item_id=b.item_id)

回答2:

Try This let me know if this works.

SELECT * 
FROM t.reports 
where item_id in (
                    select distinct item_id 
                    from t.reports
                ) 
ORDER BY updated DESC 
LIMIT 100

回答3:

Try with this I have tested it on my test database:

SELECT DISTINCT item_id, MAX(created), id, user
FROM `t.reports`
GROUP BY item_id
ORDER BY MAX(created) DESC

回答4:

You can use group by :

SELECT * FROM t.reports WHERE created IN (SELECT max(created) FROM t.reports) 
GROUP BY item_id
LIMIT 100

来源：https://stackoverflow.com/questions/44543764/how-can-i-remove-the-oldest-entries-in-my-sql-result

标签

php

mysql

pdo