Re: improving this SQL statement

"Jay" <heilongjiang__at_hotmail.com> wrote in message news:<3cba52c3_at_news.starhub.net.sg>...
> Hi,
>
> I have a very similar problem in my project and I simulate the
> situation in SCOTT/TIGER account.
>
> Appreciate if anyone can improve or suggest a better SQL
> than the one below. I somehow feel unsafe about that
> part >>
> WHERE EMPNO IN (SELECT ...);
>
> Is my concern unfounded?
> Is this a corelated UPDATE?
>
> Thank You.
>
> ================================================================
>
>
> SQL> select * from emp;
>
>
>
> EMPNO ENAME JOB MGR HIREDATE SAL COMM
> DEPTNO
>
> --------- ---------- --------- --------- --------- --------- --------- -----
> ----
>
> 7369 SMITH CLERK 7902 17-DEC-80 800
> 20
>
> 7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300
> 30
>
> 7521 WARD SALESMAN 7698 22-FEB-81 1250 500
> 30
>
> 7566 JONES MANAGER 7839 02-APR-81 2975
> 20
>
> 7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400
> 30
>
> 7698 BLAKE MANAGER 7839 01-MAY-81 2850
> 30
>
> 7782 CLARK MANAGER 7839 09-JUN-81 2450
> 10
>
> 7788 SCOTT ANALYST 7566 19-APR-87 3000
> 20
>
> 7839 KING PRESIDENT 17-NOV-81 5000
> 10
>
> 7844 TURNER SALESMAN 7698 08-SEP-81 1500 0
> 30
>
> 7876 ADAMS CLERK 7788 23-MAY-87 1100
> 20
>
> 7900 JAMES CLERK 7698 03-DEC-81 950
> 30
>
> 7902 FORD ANALYST 7566 03-DEC-81 3000
> 20
>
> 7934 MILLER CLERK 7782 23-JAN-82 1300
> 10
>
>
>
> SQL> select * from new_sal;
>
>
>
> EMPNO SAL
>
> --------- ---------
>
> 7934 2000
>
> 7900 2100
>
> 7369 2200
>
>
> update emp a
> set a.sal = (select b.sal
> from new_sal b
> where b.empno = a.empno)
> where a.empno in (select empno from new_sal);

I don't see any problem with it. You might want to replace in subquery with exists subquery if performance is a problem. Received on Mon Apr 15 2002 - 22:37:19 CEST