MYSQL - GROUP BY 2 COLUMN ORDER BY CREATION DATE

Question

I'm trying to get all results of my table with a GROUP BY on 2 columns and get the last insertions.

"Prices" table :

My Request :

SELECT DISTINCT p.*
FROM prices p 
JOIN (
SELECT MAX(created_at) as "last_created" 
FROM prices
WHERE station_id = 27210003
GROUP BY station_id, fuel_id) as sub 
ON sub.last_created = p.created_at
WHERE p.station_id = 27210003
GROUP BY p.station_id, p.fuel_id

Results are 3 lines but wrong line because not last created in my DB -_-'

Please help me !!! >_<'

Thx

Answer 1

Since you're selecting a specific station_id in the WHERE clause, you don't need to include that in GROUP BY .

The subquery has to return the columns you're grouping on, and then you have to include them in the ON clause.

And you don't need GROUP BY in the outer query, since the JOIN should ensure that there's just one row for each fuel_id (unless there are duplicate created_at for the same fuel_id and station_id ).

SELECT DISTINCT p.*
FROM prices p 
JOIN (
    SELECT fuel_id, MAX(created_at) as "last_created" 
    FROM prices
    WHERE station_id = 27210003
    GROUP BY fuel_id) as sub 
ON sub.last_created = p.created_at AND sub.fuel_id = p.fuel_id
WHERE p.station_id = 27210003