Question

I’m trying without success to solve this tricky point.
I have a mysql table like the following:

Category      Model      Description
cat1           AAA       Triple A
cat1/cat2      AAA       Triple A
cat1/cat2      BBB       Triple B
cat1           BBB       Triple B
cat3           CCC       Triple C
cat3/cat4/cat5 CCC       Triple C
cat3/cat4      CCC       Triple C

etc.

I would like to select rows with unique Model and “longest” Category. Basically I would like to obtain:

Category      Model      Description
cat1/cat2      AAA       Triple A
cat1/cat2      BBB       Triple B
cat3/cat4/cat5 CCC       Triple C

Any hint?

Answer 1

select m.*
from MyTable m
inner join (
    select Model, max(char_length(Category)) as MaxLen
    from MyTable
    group by Model
) mm on m.Model = mm.Model and char_length(m.Category) = mm.MaxLen

You may in fact, want the deepest category rather than longest. If this is the case, there are better options than above.