Question

I have a query:

SELECT emp.empno , emp.ename , emp.job , emp.sal , dept.dname , dept.loc 
  FROM emp , 
       dept 
 WHERE emp.ename = 'SMITH';

Please tell me why this is displaying all the Records , as i am expecting only one record ?

     EMPNO ENAME      JOB              SAL DNAME          LOC
---------- ---------- --------- ---------- -------------- -------------
      7369 SMITH      CLERK            800 ACCOUNTING     NEW YORK
      7369 SMITH      CLERK            800 RESEARCH       DALLAS
      7369 SMITH      CLERK            800 SALES          CHICAGO
      7369 SMITH      CLERK            800 OPERATIONS     BOSTON
      7369 SMITH      CLERK            800 CREDIT

Answer 1

The reason is because your query lacks JOIN criteria to link the two tables, so the result will be a cartesian product. Every EMP record will have a copy of every row in the DEPT table…

Your query uses ANSI-89 join syntax, which requires the criteria to be in the WHERE clause:

SELECT e.empno, e.ename, e.job, e.sal, d.dname, d.loc 
  FROM EMP e, 
       DEPT d
 WHERE d.deptno = e.deptno
   AND e.ename = 'SMITH'

But it would be preferable to use the ANSI-92 format:

SELECT e.empno, e.ename, e.job, e.sal, d.dname, d.loc 
  FROM EMP e 
  JOIN DEPT d ON d.deptno = e.deptno
 WHERE e.ename = 'SMITH'