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Oracle non-equi join

When we are joining the tables, we write the condition in ON clause using many operators. If we use any other operator other than “=” operator like (>, <, AND, OR, BETWEEN) then we call it as non-equi join.

Below is an example for non-equi join to EMP table with DEPT table.

SELECT E.*, D.*

FROM DEPT D JOIN EMP E

ON D.DEPTNO != E.DEPTNO;

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CREATE TABLE DEPT

       (DEPTNO NUMBER(2) CONSTRAINT PK_DEPT PRIMARY KEY,

        DNAME VARCHAR2(14) ,

        LOC VARCHAR2(13) ) ;

 

CREATE TABLE EMP

       (EMPNO NUMBER(4) CONSTRAINT PK_EMP PRIMARY KEY,

        ENAME VARCHAR2(10),

        JOB VARCHAR2(9),

        MGR NUMBER(4),

        HIREDATE DATE,

        SAL NUMBER(7,2),

        COMM NUMBER(7,2),

        DEPTNO NUMBER(2) CONSTRAINT FK_DEPTNO REFERENCES DEPT);

INSERT INTO DEPT VALUES (10,'ACCOUNTING','NEW YORK');

INSERT INTO DEPT VALUES (20,'RESEARCH','DALLAS');

INSERT INTO DEPT VALUES (30,'SALES','CHICAGO');

INSERT INTO DEPT VALUES (40,'OPERATIONS','BOSTON');

INSERT INTO EMP VALUES (7369,'SMITH','CLERK',7902,to_date('17-12-1980','dd-mm-yyyy'),800,NULL,20);

INSERT INTO EMP VALUES (7499,'ALLEN','SALESMAN',7698,to_date('20-2-1981','dd-mm-yyyy'),1600,300,30);

INSERT INTO EMP VALUES (7521,'WARD','SALESMAN',7698,to_date('22-2-1981','dd-mm-yyyy'),1250,500,30);

INSERT INTO EMP VALUES (7566,'JONES','MANAGER',7839,to_date('2-4-1981','dd-mm-yyyy'),2975,NULL,20);

INSERT INTO EMP VALUES (7654,'MARTIN','SALESMAN',7698,to_date('28-9-1981','dd-mm-yyyy'),1250,1400,30);

INSERT INTO EMP VALUES (7698,'BLAKE','MANAGER',7839,to_date('1-5-1981','dd-mm-yyyy'),2850,NULL,30);

INSERT INTO EMP VALUES (7782,'CLARK','MANAGER',7839,to_date('9-6-1981','dd-mm-yyyy'),2450,NULL,10);

INSERT INTO EMP VALUES (7788,'SCOTT','ANALYST',7566,to_date('13-JUL-87')-85,3000,NULL,20);

INSERT INTO EMP VALUES (7839,'KING','PRESIDENT',NULL,to_date('17-11-1981','dd-mm-yyyy'),5000,NULL,10);

INSERT INTO EMP VALUES (7844,'TURNER','SALESMAN',7698,to_date('8-9-1981','dd-mm-yyyy'),1500,0,30);

INSERT INTO EMP VALUES (7876,'ADAMS','CLERK',7788,to_date('13-JUL-87')-51,1100,NULL,20);

INSERT INTO EMP VALUES (7900,'JAMES','CLERK',7698,to_date('3-12-1981','dd-mm-yyyy'),950,NULL,30);

INSERT INTO EMP VALUES (7902,'FORD','ANALYST',7566,to_date('3-12-1981','dd-mm-yyyy'),3000,NULL,20);

INSERT INTO EMP VALUES (7934,'MILLER','CLERK',7782,to_date('23-1-1982','dd-mm-yyyy'),1300,NULL,10);

COMMIT;

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Non-equi join example for joining two tables which are Non Related

CREATE TABLE SALGRADE

      ( GRADE NUMBER,

        LOSAL NUMBER,

        HISAL NUMBER );

INSERT INTO SALGRADE VALUES (1,700,1200);

INSERT INTO SALGRADE VALUES (2,1201,1400);

INSERT INTO SALGRADE VALUES (3,1401,2000);

INSERT INTO SALGRADE VALUES (4,2001,3000);

INSERT INTO SALGRADE VALUES (5,3001,9999);

COMMIT;

oracle-non-equi-join-2

SELECT E.ENAME, E.SAL, S.GRADE

FROM EMP E JOIN SALGRADE S

ON E.SAL >= S.LOSAL AND E.SAL <= S.HISAL;

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CARTESIAN PRODUCT

If two tables in a join query have no join condition, Database returns their Cartesian product. Oracle combines each row of one table with each row of the other. A Cartesian product always generates many rows and is rarely useful. For example, the Cartesian product of two tables, each with 100 rows, has 10,000 rows. Always include a join condition unless you specifically need a Cartesian product. Cartesian product of tables EMP and DEPT will have 14x4=56 rows.  

 

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