在這點上可以用他自己帶的WITH遞歸功能,還可以用第三方擴展帶來的類似connect by 函數(shù).
先來看第一點,用遞歸的WITH來展現(xiàn)這棵樹的路徑,代碼如下:
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 --phpfensi.com ----------------------------------------------- /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 還可以用tablefunc擴展帶來的CONNECT BY函數(shù)把這棵樹遍歷出來,由于昨天設計的兩張表通過ID來關聯(lián),這個擴展自帶的函數(shù)要把名字展現(xiàn)出來比較麻煩,索性這里我就用了一張臨時表保存我想要的結果,代碼如下:
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=# 這里更新了對應的ID為NAME,代碼如下:
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擴展帶來的CONNECT BY 實現(xiàn)這棵樹的遍歷,代碼如下:
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)
