SQL statement to query all subsets and all parents

premise

mainly uses the find_in_set function, and the := operator;
If you don’t understand, you can learn about this Here is a brief explanation of the functions of these two things:
find_in_set is to determine whether a string spliced ​​with commas contains a certain string, such as : means setting the value, and then It is the same in addition, modification and query. For example, select @num:=@num+1, which means setting the num value to increase by 1. :=find_in_set('a','a,b,c'), returns the position of a in the following set, here it is 1;

Instance table:

order_num value storage rule:

Add 1 to every 9, 91 (not equal to greater than 10, otherwise there will be a problem), a>这是另个涉及排序的问题，这里不用关注.

Query all subsets

SELECT
 order_num,
 id,
 type_name ,
 ischild
FROM
 (
 SELECT
  t1.order_num,
  t1.id,
  t1.type_name,
 IF
  ( find_in_set( parent_id, @pids ) > 0, @pids := concat( @pids, ',', id ), '0' ) AS ischild 
 FROM
  ( SELECT order_num, id, type_name, parent_id FROM hw_baseinfo_project_type t WHERE del_flag = 0 ORDER BY order_num ) t1,
  ( SELECT @pids := 'f6d225fdff64e96123aaf251e1b52bc1' ) t2 
 ) t3 
WHERE
 ischild != '0' or id = 'f6d225fdff64e96123aaf251e1b52bc1' -- (带本级)
 -- ischild != '0'(不带本级)

Query all parents

SELECT
	order_num,
	id,
	type_name ,
	isParent
FROM
	(
	SELECT
		t1.order_num,
		t1.id,
		t1.type_name,
	IF
		( find_in_set( id, @ids ) > 0, @ids := concat( @ids, ',', parent_id ), '0' ) AS isParent 
	FROM
		( SELECT order_num, id, type_name, parent_id FROM hw_baseinfo_project_type t WHERE del_flag = 0 ORDER BY order_num desc) t1,
		( SELECT @ids := 'f555fe921b95ad59a35394c2d07173b7' ) t2 
	) t3 
WHERE
	isParent != '0'

Try it yourself.
当然，并不是只能传递一个值，多个值也是可以的啊

This will query the superiors of multiple subsets or the collection of subsets of multiple superiors.