昨天我用MySQL来实现了ORACLE的递归语句CONNECTBY，看起来稍复杂些。今天来看看POSTGRESQL如何实现ORACLE的CONNECTBY。还是用昨天同样的表以及数据。POSTGRESQL
昨天我用mysql来实现了oracle的递归语句connect by， 看起来稍复杂些。今天来看看postgresql如何实现oracle的connect by。
还是用昨天同样的表以及数据。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。
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。
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。
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。
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=#本文出自 “上帝，咱们不见不散！” 博客，请务必保留此出处
