Question

I have a table:


id group data
1  a     10
2  a     20
3  b     10
4  b     20


I want to get ids of records with max “data” value grouped by “group”, i.e.


id
2
4


Answer 1

Portable solution:

SELECT T1.id
FROM yourtable T1
JOIN (
    SELECT grp, MAX(data) AS data
    FROM yourtable
    GROUP BY grp
) T2
WHERE T1.grp = T2.grp AND T1.data = T2.data

PostgreSQL solution:

SELECT DISTINCT ON (grp) id
FROM yourtable
ORDER BY grp, data DESC;

PS: I changed the column name from group to grp because group is a reserved word. If you really want to use group you’ll have to quote it.