Oracle PL/SQL Tutorial/Query Select/Level

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Uses the COUNT() function and LEVEL to get the number of levels in the tree

   <source lang="sql">

SQL> SQL> SQL> SQL> SQL> -- create demo table SQL> create table Employee(

 2    EMPNO         NUMBER(3),
 3    ENAME         VARCHAR2(15 BYTE),
 4    HIREDATE      DATE,
 5    ORIG_SALARY   NUMBER(6),
 6    CURR_SALARY   NUMBER(6),
 7    REGION        VARCHAR2(1 BYTE),
 8    MANAGER_ID    NUMBER(3)
 9  )
10  /

Table created. SQL> SQL> create table job (

 2    EMPNO         NUMBER(3),
 3    jobtitle      VARCHAR2(20 BYTE)
 4  )
 5  /

Table created. SQL> SQL> insert into job (EMPNO, Jobtitle) values (1,"Tester"); 1 row created. SQL> insert into job (EMPNO, Jobtitle) values (2,"Accountant"); 1 row created. SQL> insert into job (EMPNO, Jobtitle) values (3,"Developer"); 1 row created. SQL> insert into job (EMPNO, Jobtitle) values (4,"COder"); 1 row created. SQL> insert into job (EMPNO, Jobtitle) values (5,"Director"); 1 row created. SQL> insert into job (EMPNO, Jobtitle) values (6,"Mediator"); 1 row created. SQL> insert into job (EMPNO, Jobtitle) values (7,"Proffessor"); 1 row created. SQL> insert into job (EMPNO, Jobtitle) values (8,"Programmer"); 1 row created. SQL> insert into job (EMPNO, Jobtitle) values (9,"Developer"); 1 row created. SQL> SQL> SQL> -- prepare data SQL> insert into Employee(EMPNO, EName, HIREDATE, ORIG_SALARY, CURR_SALARY, REGION, MANAGER_ID)

 2               values (1,      "Jason", to_date("19960725","YYYYMMDD"), 1234,              8767,         "E",    2)
 3  /

1 row created. SQL> insert into Employee(EMPNO, EName, HIREDATE, ORIG_SALARY, CURR_SALARY, REGION, MANAGER_ID)

 2               values (2,      "John",  to_date("19970715","YYYYMMDD"), 2341,              3456,         "W",    3)
 3  /

1 row created. SQL> insert into Employee(EMPNO, EName, HIREDATE, ORIG_SALARY, CURR_SALARY, REGION, MANAGER_ID)

 2               values (3,      "Joe",   to_date("19860125","YYYYMMDD"), 4321,              5654,         "E",    3)
 3  /

1 row created. SQL> insert into Employee(EMPNO, EName, HIREDATE, ORIG_SALARY, CURR_SALARY, REGION, MANAGER_ID)

 2               values (4,      "Tom",   to_date("20060913","YYYYMMDD"), 2413,              6787,         "W",    4)
 3  /

1 row created. SQL> insert into Employee(EMPNO, EName, HIREDATE, ORIG_SALARY, CURR_SALARY, REGION, MANAGER_ID)

 2               values (5,      "Jane",  to_date("20050417","YYYYMMDD"), 7654,              4345,         "E",    4)
 3  /

1 row created. SQL> insert into Employee(EMPNO, EName, HIREDATE, ORIG_SALARY, CURR_SALARY, REGION, MANAGER_ID)

 2               values (6,      "James", to_date("20040718","YYYYMMDD"), 5679,              6546,         "W",    5)
 3  /

1 row created. SQL> insert into Employee(EMPNO, EName, HIREDATE, ORIG_SALARY, CURR_SALARY, REGION, MANAGER_ID)

 2               values (7,      "Jodd",  to_date("20030720","YYYYMMDD"), 5438,              7658,         "E",    6)
 3  /

1 row created. SQL> insert into Employee(EMPNO, EName, HIREDATE, ORIG_SALARY, CURR_SALARY, REGION)

 2               values (8,      "Joke",  to_date("20020101","YYYYMMDD"), 8765,              4543,         "W")
 3  /

1 row created. SQL> insert into Employee(EMPNO, EName, HIREDATE, ORIG_SALARY, CURR_SALARY, REGION)

 2               values (9,      "Jack",  to_date("20010829","YYYYMMDD"), 7896,              1232,         "E")
 3  /

1 row created. SQL> SQL> SQL> SQL> -- display data in the table SQL> select * from Employee

 2  /
    EMPNO ENAME           HIREDATE  ORIG_SALARY CURR_SALARY R MANAGER_ID

--------------- --------- ----------- ----------- - ----------
        1 Jason           25-JUL-96        1234        8767 E          2
        2 John            15-JUL-97        2341        3456 W          3
        3 Joe             25-JAN-86        4321        5654 E          3
        4 Tom             13-SEP-06        2413        6787 W          4
        5 Jane            17-APR-05        7654        4345 E          4
        6 James           18-JUL-04        5679        6546 W          5
        7 Jodd            20-JUL-03        5438        7658 E          6
        8 Joke            01-JAN-02        8765        4543 W
        9 Jack            29-AUG-01        7896        1232 E

9 rows selected. SQL> select * from job

 2  /
    EMPNO JOBTITLE

--------------------
        1 Tester
        2 Accountant
        3 Developer
        4 COder
        5 Director
        6 Mediator
        7 Proffessor
        8 Programmer
        9 Developer

9 rows selected. SQL> SQL> SELECT COUNT(DISTINCT LEVEL)

 2  FROM employee
 3  START WITH empno = 1
 4  CONNECT BY PRIOR empno = manager_id;

COUNT(DISTINCTLEVEL)


                  1

SQL> SQL> SQL> -- clean the table SQL> drop table Employee

 2  /

Table dropped. SQL> drop table job

 2  /

Table dropped. SQL></source>


Using the LEVEL Pseudo-Column

   <source lang="sql">

SQL> SQL> SQL> SQL> SQL> -- create demo table SQL> create table Employee(

 2    EMPNO         NUMBER(3),
 3    ENAME         VARCHAR2(15 BYTE),
 4    HIREDATE      DATE,
 5    ORIG_SALARY   NUMBER(6),
 6    CURR_SALARY   NUMBER(6),
 7    REGION        VARCHAR2(1 BYTE),
 8    MANAGER_ID    NUMBER(3)
 9  )
10  /

Table created. SQL> SQL> create table job (

 2    EMPNO         NUMBER(3),
 3    jobtitle      VARCHAR2(20 BYTE)
 4  )
 5  /

Table created. SQL> SQL> insert into job (EMPNO, Jobtitle) values (1,"Tester"); 1 row created. SQL> insert into job (EMPNO, Jobtitle) values (2,"Accountant"); 1 row created. SQL> insert into job (EMPNO, Jobtitle) values (3,"Developer"); 1 row created. SQL> insert into job (EMPNO, Jobtitle) values (4,"COder"); 1 row created. SQL> insert into job (EMPNO, Jobtitle) values (5,"Director"); 1 row created. SQL> insert into job (EMPNO, Jobtitle) values (6,"Mediator"); 1 row created. SQL> insert into job (EMPNO, Jobtitle) values (7,"Proffessor"); 1 row created. SQL> insert into job (EMPNO, Jobtitle) values (8,"Programmer"); 1 row created. SQL> insert into job (EMPNO, Jobtitle) values (9,"Developer"); 1 row created. SQL> SQL> SQL> -- prepare data SQL> insert into Employee(EMPNO, EName, HIREDATE, ORIG_SALARY, CURR_SALARY, REGION, MANAGER_ID)

 2               values (1,      "Jason", to_date("19960725","YYYYMMDD"), 1234,              8767,         "E",    2)
 3  /

1 row created. SQL> insert into Employee(EMPNO, EName, HIREDATE, ORIG_SALARY, CURR_SALARY, REGION, MANAGER_ID)

 2               values (2,      "John",  to_date("19970715","YYYYMMDD"), 2341,              3456,         "W",    3)
 3  /

1 row created. SQL> insert into Employee(EMPNO, EName, HIREDATE, ORIG_SALARY, CURR_SALARY, REGION, MANAGER_ID)

 2               values (3,      "Joe",   to_date("19860125","YYYYMMDD"), 4321,              5654,         "E",    3)
 3  /

1 row created. SQL> insert into Employee(EMPNO, EName, HIREDATE, ORIG_SALARY, CURR_SALARY, REGION, MANAGER_ID)

 2               values (4,      "Tom",   to_date("20060913","YYYYMMDD"), 2413,              6787,         "W",    4)
 3  /

1 row created. SQL> insert into Employee(EMPNO, EName, HIREDATE, ORIG_SALARY, CURR_SALARY, REGION, MANAGER_ID)

 2               values (5,      "Jane",  to_date("20050417","YYYYMMDD"), 7654,              4345,         "E",    4)
 3  /

1 row created. SQL> insert into Employee(EMPNO, EName, HIREDATE, ORIG_SALARY, CURR_SALARY, REGION, MANAGER_ID)

 2               values (6,      "James", to_date("20040718","YYYYMMDD"), 5679,              6546,         "W",    5)
 3  /

1 row created. SQL> insert into Employee(EMPNO, EName, HIREDATE, ORIG_SALARY, CURR_SALARY, REGION, MANAGER_ID)

 2               values (7,      "Jodd",  to_date("20030720","YYYYMMDD"), 5438,              7658,         "E",    6)
 3  /

1 row created. SQL> insert into Employee(EMPNO, EName, HIREDATE, ORIG_SALARY, CURR_SALARY, REGION)

 2               values (8,      "Joke",  to_date("20020101","YYYYMMDD"), 8765,              4543,         "W")
 3  /

1 row created. SQL> insert into Employee(EMPNO, EName, HIREDATE, ORIG_SALARY, CURR_SALARY, REGION)

 2               values (9,      "Jack",  to_date("20010829","YYYYMMDD"), 7896,              1232,         "E")
 3  /

1 row created. SQL> SQL> SQL> SQL> -- display data in the table SQL> select * from Employee

 2  /
    EMPNO ENAME           HIREDATE  ORIG_SALARY CURR_SALARY R MANAGER_ID

--------------- --------- ----------- ----------- - ----------
        1 Jason           25-JUL-96        1234        8767 E          2
        2 John            15-JUL-97        2341        3456 W          3
        3 Joe             25-JAN-86        4321        5654 E          3
        4 Tom             13-SEP-06        2413        6787 W          4
        5 Jane            17-APR-05        7654        4345 E          4
        6 James           18-JUL-04        5679        6546 W          5
        7 Jodd            20-JUL-03        5438        7658 E          6
        8 Joke            01-JAN-02        8765        4543 W
        9 Jack            29-AUG-01        7896        1232 E

9 rows selected. SQL> select * from job

 2  /
    EMPNO JOBTITLE

--------------------
        1 Tester
        2 Accountant
        3 Developer
        4 COder
        5 Director
        6 Mediator
        7 Proffessor
        8 Programmer
        9 Developer

9 rows selected. SQL> SQL> SELECT LEVEL, empno, manager_id, ename

 2  FROM employee
 3  START WITH empno = 1
 4  CONNECT BY PRIOR empno = manager_id
 5  ORDER BY LEVEL;
    LEVEL      EMPNO MANAGER_ID ENAME

---------- ---------- ---------------
        1          1          2 Jason

SQL> SQL> -- clean the table SQL> drop table Employee

 2  /

Table dropped. SQL> drop table job

 2  /

Table dropped. SQL> SQL></source>