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EXISTS operator performance [message #90162] Sun, 21 November 2004 23:04
Messages: 43
Registered: September 2003
SELECT count(*)
  FROM emp
 Where exists (select 'X' From dept
                    where dname like 'A%'
                       and dept.deptno=emp.deptno)

select count(*) from emp e,dept d
where e.deptno = d.deptno
   and d.dname like 'A%'

which query is best in performance? how exists operator works?
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