Count child of every node in hier table reading source just once

Question

Hi guys,
I'm trying to write a SQL statement to count how many child every node in a hierarchical table has.
I want to perform this operation reading source table only one time.
Following an example of source table:
CREATE TABLE TEST_HIER
ID NUMBER,
PID NUMBER
Insert into TEST_HIER
(ID, PID)
Values
(1, 0);
Insert into TEST_HIER
(ID, PID)
Values
(2, 1);
Insert into TEST_HIER
(ID, PID)
Values
(3, 1);
Insert into TEST_HIER
(ID, PID)
Values
(4, 2);
Insert into TEST_HIER
(ID, PID)
Values
(5, 3);
COMMIT;
And expected result is:
PID CHILD
0 1
1 2
2 1
3 1
Any idea?
Thanks a lot
Mauro

Answer 1

maybe a CONNECT BY clause is what you are looking for.
[code] SQL> select * from emp;   EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ----- ---------- --------- ----- ----------- --------- --------- ------ 7566 JONES MANAGER 7839 02-Apr-1981 2975.00 1000.00 20 7902 FORD ANALYST 7566 03-Dec-1981 3000.00 20 7839 KING PRESIDENT 17-Nov-1981 5000.00 10 7698 BLAKE MANAGER 7839 01-May-1981 2850.00 30 7782 CLARK MANAGER 7839 09-Jun-1981 2450.00 10 7369 SMITH CLERK 7902 17-Dec-1980 800.00 20 7499 ALLEN SALESMAN 7698 20-Feb-1981 1600.00 300.00 30 7521 WARD SALESMAN 7698 22-Feb-1981 1250.00 500.00 30 7654 MARTIN SALESMAN 7698 28-Sep-1981 1250.00 1400.00 30 7788 SCOTT ANALYST 7566 09-Dec-1982 3000.00 20 7844 TURNER SALESMAN 7698 08-Sep-1981 1500.00 0.00 30 7876 ADAMS CLERK 7788 12-Jan-1983 1100.00 20 7900 JAMES CLERK 7698 03-Dec-1981 950.00 30 7934 MILLER CLERK 7782 23-Jan-1982 1300.00 10 7945 CINDY SALESMAN 7698 16-Jan-1983 1800.00 30 7950 TINA SALESMAN 7698 18-Jan-1983 1850.00 30  16 rows selected  SQL> select level, substr(lpad(' ', level+2)||ename,1,20) employee, substr(lpad(' ', level+2)||job,1,12) job 2 from emp 3 start with job = 'PRESIDENT' 4 connect by prior empno = mgr;  LEVEL EMPLOYEE JOB ---------- -------------------- ------------ 1 KING PRESIDENT 2 JONES MANAGER 3 FORD ANALYST 4 SMITH CLERK 3 SCOTT ANALYST 4 ADAMS CLERK 2 BLAKE MANAGER 3 ALLEN SALESMA 3 WARD SALESMA 3 MARTIN SALESMA 3 TURNER SALESMA 3 JAMES CLERK 3 CINDY SALESMA 3 TINA SALESMA 2 CLARK MANAGER 3 MILLER CLERK  16 rows selected  SQL>  [/code]