A question about recursion in MySQL

This article mainly introduces MySQL Recursive Small issues, friends in need can refer to it

mysql itself does not support recursive syntax, but it can be used automatically The connection implements some simple recursion in disguise

--递归小方法：临时表和普通表的不同方法
--这题使用的是2次临时表查询父节点的递归 

drop table if exists test;
create table test(
id varchar(100),
name varchar(20),
parentid varchar(100)
);
insert test select
'13ed38f1-3c24-dd81-492f-673686dff0f3', '大学教师', '37e2ea0a-1c31-3412-455a-5e60b8395f7d' union all select 
'1ce203ac-ee34-b902-6c10-c806f0f52876','小学教师', '37e2ea0a-1c31-3412-455a-5e60b8395f7d' union all select 
'37e2ea0a-1c31-3412-455a-5e60b8395f7d', '教师' ,      null                union all select 
'c877b7ea-4ed3-f472-9527-53e1618cb1dc', '高数老师', '13ed38f1-3c24-dd81-492f-673686dff0f3' union all select 
'ce50a471-2955-00fa-2fb7-198f6b45b1bd', '中学教师', '37e2ea0a-1c31-3412-455a-5e60b8395f7d';
 
delimiter $$
 
create procedure usp_ser(in idd varchar(100))
begin
declare lev int;
set lev=1;
drop table if exists tmp1;
drop table if exists tmp2;
CREATE TEMPORARY TABLE tmp1(id varchar(100),name varchar(20),parentid varchar(100),levv int);
CREATE TEMPORARY TABLE tmp2(pid varchar(100));
insert tmp2 select parentid from test where id=idd;
insert tmp1 select t.* , lev from test t join tmp2 a on t.id=a.pid;
    while exists(select 1 from tmp2 )
do
truncate tmp2;
set lev=lev+1;
insert tmp2 select t.id from test t join tmp1 a on t.id=a.parentid and a.levv=lev-1;
insert tmp1 select t.*,lev from test t join tmp2 a on t.id=a.pid;
end while ;
select id,name,parentid from tmp1;
end;
$$
 
delimiter ;
 
 call usp_ser('c877b7ea-4ed3-f472-9527-53e1618cb1dc');
+--------------------------------------+----------+--------------------------------------+
| id                  | name   | parentid               |
+--------------------------------------+----------+--------------------------------------+
| 13ed38f1-3c24-dd81-492f-673686dff0f3 | 大学教师 | 37e2ea0a-1c31-3412-455a-5e60b8395f7d |
| 37e2ea0a-1c31-3412-455a-5e60b8395f7d | 教师   | NULL                 |
+--------------------------------------+----------+--------------------------------------+
 
 call usp_ser('13ed38f1-3c24-dd81-492f-673686dff0f3');
+--------------------------------------+------+----------+
| id                  | name | parentid |
+--------------------------------------+------+----------+
| 37e2ea0a-1c31-3412-455a-5e60b8395f7d | 教师 | NULL   |
+--------------------------------------+------+----------+
 
 call usp_ser('37e2ea0a-1c31-3412-455a-5e60b8395f7d');
 
Empty set (0.02 sec)

The above method is because MySQL does not allow multiple references to the temporary table in the same statement, so use the temporary table twiceThe following Give a one-time recursive query of sub-nodes using an ordinary table

Core code

drop table if exists test;
create table test(
id INT,
parentid INT
);
insert test select
1, 0 UNION ALL SELECT 
2, 1 UNION ALL SELECT 
3, 1 UNION ALL SELECT 
4, 0 UNION ALL SELECT 
5, 2 UNION ALL SELECT 
6, 5 UNION ALL SELECT 
7, 3 ;
Go
 
delimiter $$
 
create procedure usp_ser(in idd varchar(100))
begin
declare lev int;
set lev=1;
drop table if exists tmp1;
CREATE TABLE tmp1(id INT,parentid INT ,levv INT,ppath VARCHAR(1000));

INSERT tmp1 SELECT *,lev,id FROM test WHERE parentid=idd;

 while row_count()>0
do

set lev=lev+1;
insert tmp1 select t.*,lev,concat(a.ppath,t.id) from test t join tmp1 a on t.parentid=a.id AND levv=LEV-1;
 
end while ;
SELECT * FROM tmp1;
 
end;
$$
 
delimiter ;
 
 call usp_ser(0);
 
/*
+------+----------+------+-------+
| id  | parentid | levv | ppath |
+------+----------+------+-------+
|  1 |    0 |  1 | 1   |
|  4 |    0 |  1 | 4   |
|  2 |    1 |  2 | 12  |
|  3 |    1 |  2 | 13  |
|  5 |    2 |  3 | 125  |
|  7 |    3 |  3 | 137  |
|  6 |    5 |  4 | 1256 |
+------+----------+------+-------+*/

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