postgresql 遍历参数_PostgreSQL 对简单树的遍历
昨天我用MysqL來(lái)實(shí)現(xiàn)了ORACLE的遞歸語(yǔ)句CONNECT BY， 看起來(lái)稍復(fù)雜些。今天來(lái)看看POSTGREsql如何實(shí)現(xiàn)ORACLE的CONNECT BY。
還是用昨天同樣的表以及數(shù)據(jù)。POSTGREsql自詡最像ORACLE的數(shù)據(jù)庫(kù)，所以大部分語(yǔ)句也就都可以簡(jiǎn)單而且變相的實(shí)現(xiàn)了。
在這點(diǎn)上可以用他自己帶的WITH遞歸功能，還可以用第三方擴(kuò)展帶來(lái)的類(lèi)似connect by 函數(shù)。
先來(lái)看第一點(diǎn)，用遞歸的WITH來(lái)展現(xiàn)這棵樹(shù)的路徑。
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
還可以用tablefunc擴(kuò)展帶來(lái)的CONNECT BY函數(shù)把這棵樹(shù)遍歷出來(lái)。
由于昨天設(shè)計(jì)的兩張表通過(guò)ID來(lái)關(guān)聯(lián)，這個(gè)擴(kuò)展自帶的函數(shù)要把名字展現(xiàn)出來(lái)比較麻煩，索性這里我就用了一張臨時(shí)表保存我想要的結(jié)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=#
這里更新了對(duì)應(yīng)的ID為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擴(kuò)展帶來(lái)的CONNECT BY 實(shí)現(xiàn)這棵樹(shù)的遍歷。
t_girl=# select path from connectby('tmp_country_relation as a','a.name','a.parentname','Earth','/') 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=#
總結(jié)
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