Oracle Connect By Prior（遞迴查詢）簡潔例項
阿新 • • 發佈：2019-01-26
oracle中的select語句可以用START WITH...CONNECT BY PRIOR子句實現遞迴查詢，connect by 是結構化查詢中用到的，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，用於對返回的所有記錄進行過濾。
<Conditional-2>：查詢結果重起始根結點的限定條件。
2.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;
3.如果connect by prior中的prior被省略，則查詢將不進行深層遞迴。
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;
總結： 1、start with id= 是定義起始節點（種子），可以是id也可以是root_id,定義為root_Id查詢該節點下所有的樹結構，定義為id（子節點）則查詢指定的樹 2、connect by prior ：prior的含義為先前，前一條記錄。prior id=root_id 也就是前一條記錄 的id等於當前記錄的root_id(父id)
3、可以向下或者向上查詢。。。。 4、level欄位為oracle特有的層級欄位，可以通過level欄位查詢指定的層級 select root_id,id,name,level from t2 where level=1 start with root_id = 0 connect by prior id = root_id;
select ... from <TableName>
where <Conditional-1>
start with <Conditional-2>
connect by <Conditional-3>
;
<Conditional-1>：過濾條件，用於對返回的所有記錄進行過濾。
<Conditional-2>：查詢結果重起始根結點的限定條件。
<Conditional-3>：連線條件
例如：
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');
1.獲取完整樹：
select * from t2;
select * from t2 start with root_id = 0 connect by prior id = root_id;
2.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;
3.如果connect by prior中的prior被省略，則查詢將不進行深層遞迴。
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;
總結： 1、start with id= 是定義起始節點（種子），可以是id也可以是root_id,定義為root_Id查詢該節點下所有的樹結構，定義為id（子節點）則查詢指定的樹 2、connect by prior ：prior的含義為先前，前一條記錄。prior id=root_id 也就是前一條記錄 的id等於當前記錄的root_id(父id)
3、可以向下或者向上查詢。。。。 4、level欄位為oracle特有的層級欄位，可以通過level欄位查詢指定的層級 select root_id,id,name,level from t2 where level=1 start with root_id = 0 connect by prior id = root_id;