oracle 递归查询 博客分类： 学习转贴 Oracle数据结构

Select * from …. Where [结果过滤条件语句]
Start with  [and起始条件过滤语句]
Connect by prior [and中间记录过滤条件语句]
一、Start with.........Connect By 子句
        START WITH specifies the root row(s) of the hierarchy.
         CONNECT BY specifies the relationship between parent rows and child rows of the hierarchy. In a hierarchical query, one expression in condition must be qualified with the PRIOR operator to refer to the parent row。
二、示例
1.          创建测试表：
CREATE TABLE DG_Test
(
D_ID    NUMBER, D_NAME VARCHAR2(100 BYTE), D_PID   NUMBER , D_Enabled NUMBER )

2.          插入测试数据：
INSERT NTO dg_test(D_ID,D_NAME,D_PID,D_ENABLED) VALUES(1,'10',0,1);
INSERT INTO dg_test(D_ID,D_NAME,D_PID,D_ENABLED) VALUES(2,'11',1,1);
INSERT INTO dg_test(D_ID,D_NAME,D_PID,D_ENABLED) VALUES(3,'20',0,1);
INSERT INTO dg_test(D_ID,D_NAME,D_PID,D_ENABLED) VALUES(4,'12',1,1);
INSERT INTO dg_test(D_ID,D_NAME,D_PID,D_ENABLED) VALUES(5,'121',2,1);
INSERT INTO dg_test(D_ID,D_NAME,D_PID,D_ENABLED) VALUES(6,'1215',5,0);
INSERT INTO dg_test(D_ID,D_NAME,D_PID,D_ENABLED) VALUES(7,'1214',4,0);

3.      select * from DG_Test
4.      上述单表情况一般用于维护树型结构的应用
从Root往树末梢递归
select * from dg_test
start with D_id=1
connect by prior D_id = D_pid
从末梢往树ROOT递归
select * from dg_test
start with D_id=7
connect by D_id = prior D_pid
start with 后面跟着树根，定义了树开始显示的起点位置，如上面两种查询，不管从树根到树顶，还是从树顶到树根。
5.      排除单一体及其分支
select t.* from dg_test t
start with D_id=1
connect by prior D_id = D_pid
and d_id != 2
这个语句表示从D_id为2的开始，包括后面的子分支，全部排除
注意：这里和where条件的过虑方式不一样，where条件只是把相应的某条不符合要求的记录排除。