This document will introduce the relational algebra operations of RDBMS- Core Joins, which include UNION, INTERSECT，MINUS，Outer Join（+），Self-Join 。
1.Create the test table
CREATE TABLE xx408779_departments
(depID NUMBER(38,0),
depName VARCHAR2(20),
delFlag NUMBER(1,0)
);
CREATE TABLE xx408779_employees
( empID NUMBER(38,0),
empName VARCHAR2(20),
depID NUMBER(38,0),
delFlag NUMBER(1,0)
);
INSERT INTO xx408779_departments VALUES(1,'Finacle',0);
INSERT INTO xx408779_departments VALUES(2,'Marketing',0);
INSERT INTO xx408779_departments VALUES(3,'HR',1);
INSERT INTO xx408779_departments VALUES(4,'IT',0);
INSERT INTO xx408779_departments VALUES(7,'Manufacturer',0);
INSERT INTO xx408779_employees VALUES(1,'wbq',1,0);
INSERT INTO xx408779_employees VALUES(2,'czh',2,0);
INSERT INTO xx408779_employees VALUES(3,'chh',1,0);
INSERT INTO xx408779_employees VALUES(4,'wal',2,0);
INSERT INTO xx408779_employees VALUES(5,'ddd',3,0);
INSERT INTO xx408779_employees VALUES(6,'wdfg',5,0);
2.Retrieval using UNION
SELECTd.depID,d.depName,E.empName
FROMxx408779_departmentsd,xx408779_employeesE
WHEREd.depID(+)=E.depID
UNION
SELECTd.depID,d.depName,E.empName
FROMxx408779_departmentsd,xx408779_employeesE
WHEREd.depID=E.depID(+)
3. Retrieval using INTERSECT
SELECTd.depID,d.depName,E.empName
FROMxx408779_departmentsd,xx408779_employeesE
WHEREd.depID(+)=E.depID
INTERSECT
SELECTd.depID,d.depName,E.empName
FROMxx408779_departmentsd,xx408779_employeesE
WHEREd.depID=E.depID(+)
4. Retrieval using Minus
SELECTd.depID,d.depName,E.empName
FROMxx408779_departmentsd,xx408779_employeesE
WHEREd.depID(+)=E.depID
MINUS
SELECTd.depID,d.depName,E.empName
FROMxx408779_departmentsd,xx408779_employeesE
WHEREd.depID=E.depID(+)
5.Retrieval from Multiple tables - Outer join
Example of left outer join
SELECTd.depID,d.depName,E.empName
FROMxx408779_departmentsd,xx408779_employeesE
WHEREd.depID=E.depID(+)
Example of right outer join
SELECTd.depID,d.depName,E.empName
FROMxx408779_departmentsd,xx408779_employeesE
WHEREd.depID(+)=E.depID
