如何获取自联接表的最后一个类别

Question

I have a table like this (this table is my categories of products) :

id   title   parent_id 
 1     A         0
 2     A1        1
 3     A2        1
 4     B         0
 5     A11       2
 6     B1        4

now,How can I get last of sub-categories ? for example :

B1
A11
A2

Answer 1

You seem to want the rows that are not the parent of another row:

select pc.*
from productcategories pc
where not exists (select 1
                  from productcategories pc2
                  where pc2.parent_id = pc.id
                 );