oracle中的select語句可以用START WITH...CONNECT BY PRIOR子句實作遞歸查詢，connect by 是結構化查詢中用到的，其基本文法是：
select ... from where start with connect by ;
：過濾條件，用于對傳回的所有記錄進行過濾。
：查詢結果重起始根結點的限定條件。
：連接配接條件
資料組織結構如下圖：
500)this.width=500;" >
資料庫表結構如下：
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');
擷取完整樹：
select * from t2 start with root_id = 0 connect by prior id = root_id;
500)this.width=500;" >
擷取特定子樹：
select * from t2 start with id = 1 connect by prior id = root_id;
500)this.width=500;" >
select * from t2 start with id = 4 connect by prior id = root_id;
500)this.width=500;" >
如果connect by prior中的prior被省略，則查詢将不進行深層遞歸。
如：
select * from t2 start with root_id = 0 connect by id = root_id;
500)this.width=500;" >
select * from t2 start with id = 1 connect by id = root_id;
如：
500)this.width=500;" >