update a field group by another having max of another field - mysql

Question

ID     GRP     VAL    CHK
---   -----   -----   ----
1       1       1      0
2       1       3      0
3       2       7      0
4       2       2      0
5       2       1      0
6       3       5      0

I want to set my CHK field to '1' having maximum value VAL for every group of GRP, so ID 2,3,6 should be set. I don't write my trials here, all seems rubbish :)

Answer 1

In MySQL, you can do this using the update/join syntax:

update table t join
       (select grp, max(val) as maxval
        from table t
        group by grp
       ) tmax
       on t.grp = tmax.grp and t.val = tmax.maxval
    set t.chk = 1;