CODEWITHSUNDEEP
mysql
Michal M
Michal M

Reputation: 9480

How to select only the latest rows for each user?

My table looks like this:

id  | user_id | period_id | completed_on
----------------------------------------
1   | 1       | 1         | 2010-01-01
2   | 2       | 1         | 2010-01-10
3   | 3       | 1         | 2010-01-13
4   | 1       | 2         | 2011-01-01
5   | 2       | 2         | 2011-01-03
6   | 2       | 3         | 2012-01-13
... | ...     | ...       | ...

I want to select only the latest users periods entries, bearing in mind that users will not all have the same period entries.

Essentially (assuming all I have is the above table) I want to get this:

id  | user_id | period_id | completed_on
----------------------------------------
3   | 3       | 1         | 2010-01-13
4   | 1       | 2         | 2011-01-01
6   | 2       | 3         | 2012-01-13

Both of the below queries always resulted with the first user_id occurance being selected, not the latest (because the ordering happens after the rows are selected from what I understand):

SELECT
    DISTINCT user_id,
    period_id,
    completed_on
FROM my_table
ORDER BY
    user_id ASC,
    period_id DESC

SELECT *
FROM my_table
GROUP BY user_id
ORDER BY
    user_id ASC,
    period_id DESC

Upvotes: 0

Views: 160

Answers (2)

echo_Me
echo_Me

Reputation: 37233

try this:

SELECT t.Id, t.User_Id, t.Period_Id, t.Completed_On
FROM table1 t
JOIN (SELECT Max(completed_on) Max_Completed_On, t.User_Id
FROM table1 t
GROUP BY t.User_ID) t2 ON t.User_Id = t2.User_Id AND t.Completed_On = t2.Max_Completed_On

DEMO HERE

Upvotes: 0

sgeddes
sgeddes

Reputation: 62831

Seems like this should work using MAX and a subquery:

SELECT t.Id, t.User_Id, t.Period_Id, t.Completed_On
FROM my_table t
   JOIN (SELECT Max(completed_on) Max_Completed_On, t.User_Id
         FROM my_table
         GROUP BY t.User_ID
         ) t2 ON
      t.User_Id = t2.User_Id AND t.Completed_On = t2.Max_Completed_On

However, if you potentially have multiple records where the completed_on date is the same per user, then this could return multiple records. Depending on your needs, potentially adding a MAX(Id) in your subquery and joining on that would work.

Upvotes: 2

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