postgresql菜鸟教程_PostgreSQL遍历简单树的方法教程

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还是用上次MySQL存储过程实现Oracle邻接模型树形处理的方法实例同样的表以及数据。POSTGRESQL自诩最像ORACLE的数据库，所以大部分语句也就都可以简单而且变相的实现了。

在这点上可以用他自己带的WITH递归功能，还可以用第三方扩展带来的类似connect by 函数。

 

先来看第一点，用递归的WITH来展现这棵树的路径。

 代码如下

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 on (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
(16 rows)


Time: 3.260 ms

还可以用tablefunc扩展带来的CONNECT BY函数把这棵树遍历出来。
由于昨天设计的两张表通过ID来关联，这个扩展自带的函数要把名字展现出来比较麻烦，索性这里我就用了一张临时表保存我想要的结果。

 代码如下

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=#

这里更新了对应的ID为NAME。

 代码如下
t_girl=# update tmp_country_relation set parentname = a.name from country as a where parentid = a.id;
UPDATE 15
Time: 1.829 ms

我用TABLEFUNC扩展带来的CONNECT BY 实现这棵树的遍历。

 代码如下

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
(16 rows)


Time: 5.974 ms
t_girl=#

 

 

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