A tutorial on the method of PostgreSQL traversing a simple tree

It is also the same table and data that used the last MySQL stored procedure to implement the Oracle Adjacency model tree processing method instance. PostgreSQL prides itself on being the most Oracle-like database, so most of the statements can be simple and implemented in disguise.

At this point, you can use the with recursive function of his own, and you can also use a third party extension to bring similar connect by function.

First look at the 1th, using recursive with to show the path of this tree.

The code is as follows

t_girl=# with recursive tmp_country (Id,path) as t_girl-# ( T_girl (# Select a.ID, '/' | | B.name as "path" from Country_relation as a inner join country as B in (a.id = b.id) where A.parentid is null T_girl (# UNION ALL T_girl (# Select A.id,q.path| | ' /'|| B.name as "path" from Country_relation as a inner join tmp_country as q on (q.id = A.parentid) T_girl (# INNER JOIN country as B on (a.id = b.id) T_girl (#) t_girl-# Select A.path from Tmp_country as A; Path ----------------------------------------------- /earth /earth/north America /earth/south America /earth/europe /earth/asia /earth/africa /earth/australia /earth/north America/canada /earth/north america/central America /earth/north America/island Nations /earth/north america/united States /earth/north america/united States/alabama /earth/north america/united States/alaska /earth/north america/united States/arizona /earth/north america/united States/arkansas /earth/north america/united States/california (rows) time:3.260 ms

You can also traverse the tree by using the Connect by function brought by the tablefunc extension.
Since the two tables that were designed yesterday were associated by ID, this extended self-contained function would be more cumbersome to show the name, and I would have used a temporary table to save the results I wanted.

The code is as follows
t_girl=# CREATE Temporary TABLE tmp_country_relation as SELECT B.id,a.name,b.parentid, ':: Text as ParentName from country As a,country_relation as b WHERE a.id = b.id; SELECT 16 time:11.773 ms t_girl=#

The corresponding ID, name, is updated here.

The code is as follows
t_girl=# Update tmp_country_relation Set parentname = A.name from country as a where parentid = a.id; UPDATE 15 time:1.829 ms

I used the tablefunc extension to bring the connect by to the traversal of this tree.

The code is as follows

t_girl=# Select path from Connectby (' tmp_country_relation as a ', ' a.name ', ' a.parentname ', ' earth ', 0, '/') as g (ID text, ParentID text,level Int,path text) order by level; Path ---------------------------------------------- Earth Earth/australia Earth/north America Earth/africa Earth/south America Earth/europe Earth/asia Earth/north America/island Nations Earth/north America/canada Earth/north america/central America Earth/north america/united States Earth/north america/united States/california Earth/north america/united States/arkansas Earth/north america/united States/alabama Earth/north america/united States/alaska Earth/north america/united States/arizona (rows) time:5.974 ms t_girl=#