[SQL SERVER] Hướng dẫn sử dụng hàm WITH để đệ quy trong sql

https://laptrinhvb.net/bai-viet/co-so-du-lieu/--SQL-SERVER---Huong-dan-su-dung-ham-WITH-de-de-quy-trong-sql/fcd08ab504203715.html#:~:text=%C4%90%E1%BB%87%20quy%20l%C3%A0%20qu%C3%A1%20tr%C3%ACnh,ng%C6%B0%E1%BB%9Di%20s%E1%BB%AD%20d%E1%BB%A5ng%20m%C3%A1y%20t%C3%ADnh.

https://www.youtube.com/watch?v=Mt9UEDAMXa8

 

WITH temp(id, name, alevel)
        as (
                Select id, name, 0 as aLevel
                From Category
                Where parent_id is null
                Union All
                Select b.id, b.name, a.alevel + 1
                From temp as a, Category as b
                Where a.id = b.parent_id
        )
        Select *
        From temp