oracle 递归查询

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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。