Oracle PL/SQL Tutorial/Table Joins/Self Joins
Perform outer joins in combination with self joins
<source lang="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> SQL> SELECT w.ename || " works for " ||
2 NVL(m.ename, "the shareholders") 3 FROM employee w, employee m 4 WHERE w.manager_id = m.empno;
W.ENAME||"WORKSFOR"||NVL(M.ENAME,"THESHARE
Jason works for John Joe works for Joe John works for Joe Jane works for Tom Tom works for Tom James works for Jane Jodd works for James 7 rows selected. SQL> SQL> SQL> -- clean the table SQL> drop table Employee
2 /
Table dropped. SQL> drop table job
2 /
Table dropped. SQL></source>
Self join a table
<source lang="sql">
SQL> SQL> SQL> create table employees(
2 empno NUMBER(4) 3 , ename VARCHAR2(8) 4 , init VARCHAR2(5) 5 , job VARCHAR2(8) 6 , mgr NUMBER(4) 7 , bdate DATE 8 , msal NUMBER(6,2) 9 , comm NUMBER(6,2) 10 , deptno NUMBER(2) ) ;
Table created. SQL> SQL> SQL> insert into employees values(1,"Jason", "N", "TRAINER", 2, date "1965-12-18", 800 , NULL, 10); 1 row created. SQL> insert into employees values(2,"Jerry", "J", "SALESREP",3, date "1966-11-19", 1600, 300, 10); 1 row created. SQL> insert into employees values(3,"Jord", "T" , "SALESREP",4, date "1967-10-21", 1700, 500, 20); 1 row created. SQL> insert into employees values(4,"Mary", "J", "MANAGER", 5, date "1968-09-22", 1800, NULL, 20); 1 row created. SQL> insert into employees values(5,"Joe", "P", "SALESREP",6, date "1969-08-23", 1900, 1400, 30); 1 row created. SQL> insert into employees values(6,"Black", "R", "MANAGER", 7, date "1970-07-24", 2000, NULL, 30); 1 row created. SQL> insert into employees values(7,"Red", "A", "MANAGER", 8, date "1971-06-25", 2100, NULL, 40); 1 row created. SQL> insert into employees values(8,"White", "S", "TRAINER", 9, date "1972-05-26", 2200, NULL, 40); 1 row created. SQL> insert into employees values(9,"Yellow", "C", "DIRECTOR",10, date "1973-04-27", 2300, NULL, 20); 1 row created. SQL> insert into employees values(10,"Pink", "J", "SALESREP",null,date "1974-03-28", 2400, 0, 30); 1 row created. SQL> SQL> SQL> SQL> select e.ename as employee
2 , m.ename as manager 3 from employees m 4 JOIN 5 employees e 6 ON e.mgr = m.empno 7 where e.bdate > date "1965-01-01" 8 order by employee;
EMPLOYEE MANAGER
--------
Black Red Jason Jerry Jerry Jord Joe Black Jord Mary Mary Joe Red White White Yellow Yellow Pink 9 rows selected. SQL> SQL> drop table employees; Table dropped. SQL> SQL></source>
Understanding Self Joins
A self join is a join made on the same table.
To perform a self join, you must use a different table alias.
<source lang="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> SQL> SQL> SELECT w.ename || " works for "|| " " || m.ename
2 FROM employee w, employee m 3 WHERE w.manager_id = m.empno;
W.ENAME||"WORKSFOR"||""||M.ENAME
Jason works for John Joe works for Joe John works for Joe Jane works for Tom Tom works for Tom James works for Jane Jodd works for James 7 rows selected. SQL> SQL> -- clean the table SQL> drop table Employee
2 /
Table dropped. SQL> drop table job
2 /
Table dropped. SQL></source>
