Oracle層次查詢（connect by ）是結(jié)構(gòu)化查詢中用到的，下面就為您介紹Oracle層次查詢的基本語法，希望可以讓您對Oracle層次查詢有更深的認(rèn)識。

oracle中的select語句可以用START WITH...CONNECT BY PRIOR子句實現(xiàn)遞歸查詢，connect by 是結(jié)構(gòu)化查詢中用到的，其基本語法是：

select ... from <TableName>
where <Conditional-1>
start with <Conditional-2>
connect by <Conditional-3>
;
<Conditional-1>：過濾條件，用于對返回的所有記錄進(jìn)行過濾。
<Conditional-2>：查詢結(jié)果重起始根結(jié)點的限定條件。
<Conditional-3>：連接條件

數(shù)據(jù)組織結(jié)構(gòu)如下圖：

數(shù)據(jù)庫表結(jié)構(gòu)如下：

create table t2(
root_id number,
id number,
name varchar(5),
description varchar(10)
);

insert into t2(root_id,id,name,description) values(0,1,'a','aaa');
insert into t2(root_id,id,name,description) values(1,2,'a1','aaa1');
insert into t2(root_id,id,name,description) values(1,3,'a2','aaa2');
insert into t2(root_id,id,name,description) values(0,4,'b','bbb');
insert into t2(root_id,id,name,description) values(4,5,'b1','bbb1');
insert into t2(root_id,id,name,description) values(4,6,'b2','bbb2');

獲取完整樹：
select * from t2 start with root_id = 0 connect by prior id = root_id;

獲取特定子樹：
select * from t2 start with id = 1 connect by prior id = root_id;

select * from t2 start with id = 4 connect by prior id = root_id;

如果connect by prior中的prior被省略，則查詢將不進(jìn)行深層遞歸。
如：

select * from t2 start with root_id = 0 connect by id = root_id;

select * from t2 start with id = 1 connect by id = root_id;
如：

【編輯推薦】

oracle查詢中表的連接順序

oracle查詢用戶所有表的語句

常見的ORACLE數(shù)據(jù)類型介紹

查詢Oracle日志文件的方法

Oracle索引的優(yōu)化設(shè)計