select unique row as per latest created_at time - mysql

Question

this is my query:
SELECT br.employee_id AS rat_id,
br.rating_comment,
br.created_at,
br.id
FROM employee_followers
LEFT JOIN employee_ratings AS br ON employee_followers. employee_id = br.employee_id
WHERE employee_followers.employee_id IN
(SELECT `employee_id`
FROM employee_followers
WHERE user_id =32)
GROUP BY br.id
ORDER BY created_at DESC
what I am getting:
rat_id rating_comment created_at id
18 superb developer 2016-02-19 18:26:54 82
9 james to manoj-joshi 2016-02-19 16:42:17 84
50 james to prem 2016-02-19 13:05:30 83
50 pinal to prem 2016-02-19 12:20:00 73
50 prem to premal-joshi 2016-02-19 11:40:52 78
18 prem to mukund 2016-02-19 11:21:52 77
18 pinal to mukund 2016-02-18 11:37:00 76
9 mukund rate to mitesh 2016-02-15 22:34:14 51
9 Not a bad. 2016-02-10 00:16:31 45
9 sda 2016-02-08 01:36:33 39
what I want:
rat_id rating_comment created_at id
18 superb developer 2016-02-19 18:26:54 82
9 james to manoj-joshi 2016-02-19 16:42:17 84
50 james to prem 2016-02-19 13:05:30 83

Answer 1

Try This
SELECT rat_id,rating_comment, MAX(created_at) AS created, id FROM (
SELECT br.employee_id AS rat_id,
br.rating_comment,
br.created_at,
br.id
FROM employee_followers
LEFT JOIN employee_ratings AS br ON employee_followers. employee_id = br.employee_id
WHERE employee_followers.employee_id IN
(SELECT `employee_id`
FROM employee_followers
WHERE user_id =32)
GROUP BY br.id
ORDER BY created_at DESC) AS temp GROUP BY temp.rat_id

Answer 2

It seems that you want only the latest record per employee_id. You can use a derived table to get the maximum date, then join again to get all fields from employee_ratings table for this date:
SELECT er.employee_id AS rat_id,
er.rating_comment,
er.created_at,
er.id
FROM employee_followers AS ef
LEFT JOIN (
SELECT employee_id, MAX(created_at) AS max_date
FROM employee_ratings
GROUP BY employee_id
) AS emp_max ON ef.employee_id = emp_max.employee_id
LEFT JOIN employee_ratings AS er
ON emp_max.employee_id = er.employee_id AND
emp_max.max_date = er.max_date
WHERE user_id = 32
ORDER BY created_at DESC
I have also removed GROUP BY br.id that seems to be redundant in the context of the query. Also IN operator can be replaced by user_id = 32 since you are selecting from the same table.