层次查询
create table emp_hire as
select empno,mgr,ename from emp
select * from emp_hire
EMPNO MGR ENAME
5555 7900 ggg
7369 7902 SMITH
7499 7698 ALLEN
7521 7698 WARD
7566 7839 JONES
7654 7698 MA & RTIN
7698 7839 BLAKE
7782 7839 CLARK
7788 7566 SCOTT
7839 KING
7844 7698 TURNER
7900 7698 JAMES
7902 7566 FORD
7934 7782 MILLER
7876 7788 ADAMS
这些数据存在着层次关系
select
lpad('*',level,'*')||e.ename ename,
e.empno,
mgr fa_id,
(select ename from emp_hire where empno=e.mgr) fa_name
from emp_hire e
START WITH MGR IS NULL
CONNECT BY PRIOR EMPNO = MGR
ENAME EMPNO FA_ID FA_NAME
*KING 7839
**JONES 7566 7839 KING
***SCOTT 7788 7566 JONES
****ADAMS 7876 7788 SCOTT
***FORD 7902 7566 JONES
****SMITH 7369 7902 FORD
**BLAKE 7698 7839 KING
***ALLEN 7499 7698 BLAKE
***WARD 7521 7698 BLAKE
***MA & RTIN 7654 7698 BLAKE
***TURNER 7844 7698 BLAKE
***JAMES 7900 7698 BLAKE
****ggg 5555 7900 JAMES
**CLARK 7782 7839 KING
***MILLER 7934 7782 CLARK
其中
start with -- this identifies all LEVEL=1 nodes in the tree
connect by -- describes how to walk from the parent nodes above to their children and their childrens children.
层次是一棵树， 又如同一个家族图谱
每一个子节电只有一个父节点；
每一个分支，最末端是叶节点；
SELECT
ename Employee,
CONNECT_BY_ISLEAF IsLeaf,
LEVEL lev,
SYS_CONNECT_BY_PATH(ename, '/') Path
FROM emp
START WITH MGR IS NULL
CONNECT BY PRIOR EMPNO = MGR
EMPLOYEE ISLEAF LEV PATH
KING 0 1 /KING
JONES 0 2 /KING/JONES
SCOTT 0 3 /KING/JONES/SCOTT
ADAMS 1 4 /KING/JONES/SCOTT/ADAMS
FORD 0 3 /KING/JONES/FORD
SMITH 1 4 /KING/JONES/FORD/SMITH
BLAKE 0 2 /KING/BLAKE
ALLEN 1 3 /KING/BLAKE/ALLEN
WARD 1 3 /KING/BLAKE/WARD
MA & RTIN 1 3 /KING/BLAKE/MA & RTIN
TURNER 1 3 /KING/BLAKE/TURNER
JAMES 0 3 /KING/BLAKE/JAMES
ggg 1 4 /KING/BLAKE/JAMES/ggg
CLARK 0 2 /KING/CLARK
MILLER 1 3 /KING/CLARK/MILLER
检查一个层次是否存在闭循环
CONNECT_BY_ISCYCLE
找出根节点
CONNECT_BY_ROOT
SELECT
ename Employee,
CONNECT_BY_ISCYCLE,
CONNECT_BY_ROOT ename
FROM emp
START WITH MGR IS NULL
CONNECT BY NOCYCLE PRIOR EMPNO = MGR
EMPLOYEE CONNECT_BY_ISCYCLE CONNECT_BY_ROOTENAME
KING 0 KING
JONES 0 KING
SCOTT 0 KING
ADAMS 0 KING
FORD 0 KING
SMITH 0 KING
BLAKE 0 KING
ALLEN 0 KING
WARD 0 KING
MA & RTIN 0 KING
TURNER 0 KING
JAMES 0 KING
ggg 0 KING
CLARK 0 KING
MILLER 0 KING
层次查询的过滤条件
SELECT
ename Employee,
CONNECT_BY_ISLEAF IsLeaf,
LEVEL lev,
SYS_CONNECT_BY_PATH(ename, '/') Path
FROM emp
where level<3
START WITH MGR IS NULL
CONNECT BY PRIOR EMPNO = MGR
Restriction on LEVEL in WHERE Clauses In a [NOT] IN condition in a WHERE clause, if the right-hand side of the condition is a subquery, you cannot use LEVEL on the left-hand side of the condition. However, you can specify LEVEL in a subquery of the FROM clause to achieve the same result. For example, the following statement is not valid:
SELECT employee_id, last_name FROM employees
WHERE (employee_id, LEVEL)
IN (SELECT employee_id, 2 FROM employees)
START WITH employee_id = 2
CONNECT BY PRIOR employee_id = manager_id;
But the following statement is valid because it encapsulates the query containing the
LEVEL information in the FROM clause:
SELECT v.employee_id, v.last_name, v.lev
FROM
(SELECT employee_id, last_name, LEVEL lev
FROM employees v
START WITH employee_id = 100
CONNECT BY PRIOR employee_id = manager_id) v
WHERE (v.employee_id, v.lev) IN
(SELECT employee_id, 2 FROM employees);
SIBLINGS的排序
SELECT
ename Employee,
CONNECT_BY_ISLEAF IsLeaf,
LEVEL lev,
SYS_CONNECT_BY_PATH(ename, '/') Path
FROM emp
START WITH MGR IS NULL
CONNECT BY PRIOR EMPNO = MGR
ORDER SIBLINGS BY ename desc
EMPLOYEE ISLEAF LEV PATH
KING 0 1 /KING
JONES 0 2 /KING/JONES
SCOTT 0 3 /KING/JONES/SCOTT
ADAMS 1 4 /KING/JONES/SCOTT/ADAMS
FORD 0 3 /KING/JONES/FORD
SMITH 1 4 /KING/JONES/FORD/SMITH
CLARK 0 2 /KING/CLARK
MILLER 1 3 /KING/CLARK/MILLER
BLAKE 0 2 /KING/BLAKE
WARD 1 3 /KING/BLAKE/WARD
TURNER 1 3 /KING/BLAKE/TURNER
MA & RTIN 1 3 /KING/BLAKE/MA & RTIN
JAMES 0 3 /KING/BLAKE/JAMES
ggg 1 4 /KING/BLAKE/JAMES/ggg
ALLEN 1 3 /KING/BLAKE/ALLEN
注意：ORDER SIBLINGS By一定与start with 与 connect by一起使用
检查树是否有闭循环
SELECT last_name "Employee", CONNECT_BY_ISCYCLE "Cycle",
LEVEL, SYS_CONNECT_BY_PATH(last_name, '/') "Path"
FROM employees
WHERE level <= 3 AND department_id = 80
START WITH last_name = 'King'
CONNECT BY NOCYCLE PRIOR employee_id = manager_id AND LEVEL <= 4;
Employee Cycle LEVEL Path
King 0 1 /King
Russell 0 2 /King/Russell
Tucker 0 3 /King/Russell/Tucker
Bernstein 0 3 /King/Russell/Bernstein
Hall 0 3 /King/Russell/Hall
Olsen 0 3 /King/Russell/Olsen
Cambrault 0 3 /King/Russell/Cambrault
Tuvault 0 3 /King/Russell/Tuvault
Partners 0 2 /King/Partners
King 0 3 /King/Partners/King
层次查询的累计运算
将非叶节点的度量sal置为空
update emp_hire set sal=null
where empno in
(
select empno from
(
SELECT
empno,
CONNECT_BY_ISLEAF IsLeaf,
LEVEL lev,
SYS_CONNECT_BY_PATH(ename, '/') Path
FROM emp
START WITH MGR IS NULL
CONNECT BY PRIOR EMPNO = MGR
)
where isleaf=0
)
察看数据
SELECT
empno,
CONNECT_BY_ISLEAF IsLeaf,
LEVEL lev,
SYS_CONNECT_BY_PATH(ename, '/') Path,
sal
FROM emp_hire
START WITH MGR IS NULL
CONNECT BY PRIOR EMPNO = MGR
EMPNO ISLEAF LEV PATH SAL
7839 0 1 /KING
7566 0 2 /KING/JONES
7788 0 3 /KING/JONES/SCOTT
7876 1 4 /KING/JONES/SCOTT/ADAMS 1100.00
7902 0 3 /KING/JONES/FORD
7369 1 4 /KING/JONES/FORD/SMITH 800.00
7698 0 2 /KING/BLAKE
7499 1 3 /KING/BLAKE/ALLEN 1600.00
7521 1 3 /KING/BLAKE/WARD 1250.00
7654 1 3 /KING/BLAKE/MA & RTIN 1250.00
7844 1 3 /KING/BLAKE/TURNER 1500.00
7900 0 3 /KING/BLAKE/JAMES
5555 1 4 /KING/BLAKE/JAMES/ggg 0.00
7782 0 2 /KING/CLARK
7934 1 3 /KING/CLARK/MILLER 1300.00
select
sum(sal),
sum(power(0.5,(level-1))*sal)
from emp_hire
START WITH MGR IS NULL
CONNECT BY PRIOR EMPNO = MGR
SUM(SAL) SUM(POWER(0.5,(LEVEL-1))*SAL)
8800 1962.5
我们不能用以下的方法计算累计值
select
SYS_CONNECT_BY_PATH(ename, '/') Path, sum(sal),
sum(power(0.5,(level-1))*sal)
from emp_hire
START WITH MGR IS NULL
CONNECT BY PRIOR EMPNO = MGR
group by Path
我们可以找出一个节点的所有子孙节点，以及这些节点所在的level
select
empno,
SYS_CONNECT_BY_PATH(ename, '/') Path, sal,
--,sum(power(0.5,(level-1))*sal)
(
select sum(power(0.5,(level-1))*nvl(sal,0)) from emp_hire
start with empno=e.empno
connect by prior empno= mgr
) s_sal,
(
select sum(nvl(sal,0)) from emp_hire
start with empno=e.empno
connect by prior empno= mgr
) s1_sal
from emp_hire e
START WITH MGR IS NULL
CONNECT BY PRIOR EMPNO = MGR
EMPNO PATH SAL S_SAL S1_SAL
7839 /KING 1962.5 8800
7566 /KING/JONES 475 1900
7788 /KING/JONES/SCOTT 550 1100
7876 /KING/JONES/SCOTT/ADAMS 1100.00 1100 1100
7902 /KING/JONES/FORD 400 800
7369 /KING/JONES/FORD/SMITH 800.00 800 800
7698 /KING/BLAKE 2800 5600
7499 /KING/BLAKE/ALLEN 1600.00 1600 1600
7521 /KING/BLAKE/WARD 1250.00 1250 1250
7654 /KING/BLAKE/MA & RTIN 1250.00 1250 1250
7844 /KING/BLAKE/TURNER 1500.00 1500 1500
7900 /KING/BLAKE/JAMES 0 0
5555 /KING/BLAKE/JAMES/ggg 0.00 0 0
7782 /KING/CLARK 650 1300
7934 /KING/CLARK/MILLER 1300.00 1300 1300
也可以通过以下过程实现：
create type myTable is table of varchar2(100);
CREATE OR REPLACE FUNCTION str_to_table (
string_in IN VARCHAR2 ,
delimiter_in IN VARCHAR2 DEFAULT ','
) RETURN myTable IS
v_wkg_str VARCHAR2 ( 32767 ) := string_in || delimiter_in;
v_pos PLS_INTEGER ;
nt_return myTable := myTable();
i_count pls_integer;
BEGIN
LOOP
v_pos := INSTR(v_wkg_str,delimiter_in);
EXIT WHEN NVL(v_pos, 0 ) = 0 or v_wkg_str=delimiter_in;
if TRIM (SUBSTR(v_wkg_str, 1 ,v_pos- 1 )) is not null then
nt_return. EXTEND ;
nt_return(nt_return. LAST ) := TRIM (SUBSTR(v_wkg_str, 1 ,v_pos- 1 ));
end if;
v_wkg_str := SUBSTR(v_wkg_str,v_pos+ 1 );
END LOOP ;
RETURN nt_return;
END ;
declare
--create or replace type v2 is table of varchar2(2000)
c_path v2;
c_level v1;
c_empno v1;
v_pos integer;
v_string varchar2(2000);
begin
select
empno,SYS_CONNECT_BY_PATH(empno, '/') Path, level lev
bulk collect into c_empno,c_path,c_level
from emp_hire
START WITH MGR IS NULL
CONNECT BY PRIOR EMPNO = MGR;
for i in 1..c_empno.count loop
v_string:='';
for j in 1..c_path.count loop
v_pos := INSTR(c_path(j),c_empno(i));
if v_pos>0 and c_empno(i)<>c_empno(j) then
v_string:=v_string||'/'||c_empno(j);
end if;
end loop;
dbms_output.put_line(c_empno(i)||' '||v_string);
end loop;
end;
输出结果
7839 /7566/7788/7876/7902/7369/7698/7499/7521/7654/7844/7900/5555/7782/7934
7566 /7788/7876/7902/7369
7788 /7876
7876
7902 /7369
7369
7698 /7499/7521/7654/7844/7900/5555
7499
7521
7654
7844
7900 /5555
5555
7782 /7934
7934
如果要计算累计结果则
declare
--create or replace type v2 is table of varchar2(2000)
c_path v2;
c_level v1;
c_empno v1;
c_sal v1;
v_pos integer;
v_string varchar2(2000);
v_sal number;
begin
select
empno,SYS_CONNECT_BY_PATH(empno, '/') Path, level lev, nvl(sal,0)
bulk collect into c_empno,c_path,c_level,c_sal
from emp_hire
START WITH MGR IS NULL
CONNECT BY PRIOR EMPNO = MGR;
for i in 1..c_empno.count loop
v_string:='';
v_sal:=0;
for j in 1..c_path.count loop
v_pos := INSTR(c_path(j),c_empno(i));
if v_pos>0 then
if c_empno(i)<>c_empno(j) then
v_string:=v_string||'/'||c_empno(j);
end if;
v_sal:=v_sal+c_sal(j);
end if;
end loop;
dbms_output.put_line(c_empno(i)||' '||v_string||' '||v_sal);
end loop;
end;
7839 8800 /7566/7788/7876/7902/7369/7698/7499/7521/7654/7844/7900/5555/7782/7934
7566 1900 /7788/7876/7902/7369
7788 1100 /7876
7876 1100
7902 800 /7369
7369 800
7698 5600 /7499/7521/7654/7844/7900/5555
7499 1600
7521 1250
7654 1250
7844 1500
7900 0 /5555
5555 0
7782 1300 /7934
7934 1300
如果存在一定的累计规则
则
declare
--create or replace type v2 is table of varchar2(2000)
c_path v2;
c_level v1;
c_empno v1;
c_sal v1;
v_pos integer;
v_string varchar2(2000);
v_sal number;
begin
select
empno,SYS_CONNECT_BY_PATH(empno, '/') Path, level lev, nvl(sal,0)
bulk collect into c_empno,c_path,c_level,c_sal
from emp_hire
START WITH MGR IS NULL
CONNECT BY PRIOR EMPNO = MGR;
for i in 1..c_empno.count loop
v_string:='';
v_sal:=0;
for j in 1..c_path.count loop
v_pos := INSTR(c_path(j),c_empno(i));
if v_pos>0 then
if c_empno(i)<>c_empno(j) then
v_string:=v_string||'/'||c_empno(j);
end if;
v_sal:=v_sal+power(0.5,(c_level(j)-c_level(i)))*c_sal(j);
end if;
end loop;
dbms_output.put_line(c_empno(i)||' '||' '||c_sal(i)||' '||v_sal||' '||v_string);
end loop;
end;
7839 0 1962.5 /7566/7788/7876/7902/7369/7698/7499/7521/7654/7844/7900/5555/7782/7934
7566 0 475 /7788/7876/7902/7369
7788 0 550 /7876
7876 1100 1100
7902 0 400 /7369
7369 800 800
7698 0 2800 /7499/7521/7654/7844/7900/5555
7499 1600 1600
7521 1250 1250
7654 1250 1250
7844 1500 1500
7900 0 0 /5555
5555 0 0
7782 0 650 /7934
7934 1300 1300
-----------------------------------------------------------------------------------------------------------
SELECT
empno,
ename Employee,
CONNECT_BY_ROOT ename,
level lev
FROM (select * from emp_hire where ename<>'KING')
START WITH MGR IS NULL
CONNECT BY NOCYCLE PRIOR EMPNO = MGR
层次查询的效率
Explain plan for
select
lpad('*',level,'*')||e.ename ename,
e.empno,
mgr fa_id
from emp_hire e
START WITH MGR IS NULL
CONNECT BY PRIOR EMPNO = MGR
select * from table(dbms_xplan.display());
Plan hash value: 2148023842
----------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 15 | 495 | 3 (0)| 00:00:01 |
|* 1 | CONNECT BY NO FILTERING WITH START-WITH| | | | | |
| 2 | TABLE ACCESS FULL | EMP_HIRE | 15 | 495 | 3 (0)| 00:00:01 |
----------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("MGR"=PRIOR "EMPNO")
filter("MGR" IS NULL)
Note
-----
- dynamic sampling used for this statement
层次查询从本质上来说是递归运算，因此对于大的层次查询，可以分解为多个层次查询，从而减少计算量。
层次查询的副产品
产生自然数的查询
select rownum r from dual connect by level <= 100
层次向普通对称维度表的转换
