Oracle Connect By用法

oracle中的select语句可以用START WITH...CONNECT BY PRIOR子句实现递归查询，connect by 是结构化查询中用到的，其基本语法是：

select ... from <TableName>

where <Conditional-1>

start with <Conditional-2>

connect by <Conditional-3>

;

<Conditional-1>：过滤条件，用于对返回的所有记录进行过滤。

<Conditional-2>：查询结果重起始根结点的限定条件。

<Conditional-3>：连接条件

数据组织结构如下图：

|---a------a1

| |------a2

|

|---b------b1

|------b2

数据库表结构如下：

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');

SQL> select * from t2;

ROOT_ID ID NAME DESCRIPTIO

---------- ---------- ----- ----------

0 1 a aaa

1 2 a1 aaa1

1 3 a2 aaa2

0 4 b bbb

4 5 b1 bbb1

4 6 b2 bbb2

获取完整树：

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

|---a------a1

| |------a2

|

|---b------b1

|------b2

ROOT_ID ID NAME DESCRIPTIO

---------- ---------- ----- ----------

0 1 a aaa

1 2 a1 aaa1

1 3 a2 aaa2

0 4 b bbb

4 5 b1 bbb1

4 6 b2 bbb2

获取特定子树：

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

|---a------a1

| |------a2

ROOT_ID ID NAME DESCRIPTIO

---------- ---------- ----- ----------

0 1 a aaa

1 2 a1 aaa1

1 3 a2 aaa2

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

|---b------b1

|------b2

ROOT_ID ID NAME DESCRIPTIO

---------- ---------- ----- ----------

0 4 b bbb

4 5 b1 bbb1

4 6 b2 bbb2

如果connect by prior中的prior被省略，则查询将不进行深层递归。

如：

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

|---a

|

|

|---b

ROOT_ID ID NAME DESCRIPTIO

---------- ---------- ----- ----------

0 1 a aaa

0 4 b bbb

如：

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

|---a

ROOT_ID ID NAME DESCRIPTIO

---------- ---------- ----- ----------

0 1 a aaa

level,connect_by_isleaf,connect_by_iscycle伪列
level 就是这个数据属于哪一个等级，比如PRESIDENT为1，MANAGER为2
connect_by_isleaf 就是树的最末端的值，或者说这个树枝下已经没有树叶了
connect_by_iscycle 导致出现死循环的那个树枝

查询scott 的emp 表
SQL> select empno,level,rpad('*',level,'*')||ename name,job,mgr from emp start with empno=7839 connect by prior empno=mgr;

EMPNO LEVEL NAME JOB MGR

----- ---------- ------------ --------- -----

7839 1 *KING PRESIDENT --level 为1

7566 2 **JONES MANAGER 7839 --level 为2

7788 3 ***SCOTT ANALYST 7566

7876 4 ****ADAMS CLERK 7788

7902 3 ***FORD ANALYST 7566

7369 4 ****SMITH CLERK 7902

7698 2 **BLAKE MANAGER 7839

7499 3 ***ALLEN SALESMAN 7698

7521 3 ***WARD SALESMAN 7698

7654 3 ***MARTIN SALESMAN 7698

7844 3 ***TURNER SALESMAN 7698

7900 3 ***JAMES CLERK 7698

7782 2 **CLARK MANAGER 7839

7934 3 ***MILLER CLERK 7782

--认为的创造一个错误的数据

update
emp set
mgr=7902
where
empno=7839;
commit;
--现在的数据变成了

SQL> select * from emp;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO

----- ---------- --------- ----- ----------- --------- --------- ------

7369 SMITH CLERK 7902 1980-12-17 800.00 20

7499 ALLEN SALESMAN 7698 1981-02-20 1600.00 300.00 30

7521 WARD SALESMAN 7698 1981-02-22 1250.00 500.00 30

7566 JONES MANAGER 7839 1981-04-02 2975.00 20

7654 MARTIN SALESMAN 7698 1981-09-28 1250.00 1400.00 30

7698 BLAKE MANAGER 7839 1981-05-01 2850.00 30

7782 CLARK MANAGER 7839 1981-06-09 2450.00 10

7788 SCOTT ANALYST 7566 1987-04-19 3000.00 20

7839 KING PRESIDENT 7902 1981-11-17 5000.00 10

7844 TURNER SALESMAN 7698 1981-09-08 1500.00 0.00 30

7876 ADAMS CLERK 7788 1987-05-23 1100.00 20

7900 JAMES CLERK 7698 1981-12-03 950.00 30

7902 FORD ANALYST 7566 1981-12-03 3000.00 20

7934 MILLER CLERK 7782 1982-01-23 1300.00 10

SQL> select empno,rpad('*',level,'*')||ename name,job,mgr,sal from emp start with empno=7839 connect by prior empno=mgr;

select empno,rpad('*',level,'*')||ename name,job,mgr,sal from emp start with empno=7839 connect by prior empno=mgr

ORA-01436:
用户数据中的 CONNECT BY
循环

SQL> select empno,

2 level,

3 CONNECT_BY_ISLEAF isleaf ,

4 connect_by_iscycle iscycle,

5 rpad('*', level, '*') || ename name,

6 job,

7 mgr

8 from emp

9 start with empno = 7839

10 connect by nocycle prior empno = mgr;

EMPNO LEVEL ISLEAF ISCYCLE NAME JOB MGR

----- ---------- ---------- ---------- ------------ --------- -----

7839 1 0 0 *KING PRESIDENT 7902

7566 2 0 0 **JONES MANAGER 7839

7788 3 0 0 ***SCOTT ANALYST 7566

7876 4 1 0 ****ADAMS CLERK 7788

7902 3 0 1 ***FORD ANALYST 7566 --这一行和第一行死循环了

7369 4 1 0 ****SMITH CLERK 7902

7698 2 0 0 **BLAKE MANAGER 7839

7499 3 1 0 ***ALLEN SALESMAN 7698

7521 3 1 0 ***WARD SALESMAN 7698 --这个是树枝的末端了

7654 3 1 0 ***MARTIN SALESMAN 7698

7844 3 1 0 ***TURNER SALESMAN 7698

7900 3 1 0 ***JAMES CLERK 7698

7782 2 0 0 **CLARK MANAGER 7839

7934 3 1 0 ***MILLER CLERK 7782