Question

I have a cat table that has the following columns:

cat_id  | name            |   parent_id
1         cat1                1
2         subcat1             1
3         subcat1-subcat      2

This table has thousands of categories but that is the general structure.

When a user selects a top level category I have a query to get its children like this:

SELECT * FROM cat WHERE parent = $id

My problem is that I need to know if these children categories have children of their own.

I could do a loop on the results and do a query for each category returned, but I am hoping that there is a solution where I can use just one query, maybe it will require a sub query?

Thanks for the help.

Answer 1

You could use a subquery to check if there are child nodes:

select  *
,       case 
        when exists (select * from cat c2 where c2.parent_id = c1.cat_id) then 0
        else 1
        end as HasSubcategories
from    cat c1