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  1. SELECT  *
  2. FROM    emp E
  3. WHERE   E.sal > 50000
  4. AND 25 > (SELECT COUNT(*)
  5.         FROM emp M
  6.         WHERE M.mgr = E.empno);
  7. -- CPU = 156 detik --
  8.  
  9. SELECT  *
  10. FROM    emp E
  11. WHERE   25 > (SELECT COUNT(*)
  12.         FROM emp M
  13.         WHERE M.mgr = E.empno)
  14. AND E.sal > 50000;
  15. -- CPU = 10 detik --
  16.  
  17. SELECT  *
  18. FROM    emp E
  19. WHERE   25 > (SELECT COUNT(*)
  20.         FROM emp M
  21.         WHERE M.mgr = E.empno)
  22. OR  E.sal > 50000;
  23. -- CPU = 100 detik --
  24.  
  25. SELECT  *
  26. FROM    emp E
  27. WHERE   E.sal > 50000
  28. OR  25 > (SELECT COUNT(*)
  29.         FROM emp M
  30.         WHERE M.mgr = E.empno);
  31. -- CPU = 30 detik --
  32.  
  33. SELECT deptno,
  34.        AVG(sal)
  35. FROM   emp
  36. GROUP  BY deptno
  37. HAVING deptno IN (10, 20);
  38. -- Having: Baris akan disaring setelah hasilnya di return --
  39.  
  40.  
  41. SELECT deptno,
  42.        AVG(sal)
  43. FROM   emp
  44. WHERE  deptno IN (10, 20)
  45. GROUP  BY deptno;
  46. -- Where: baris disaring duluan/hasil lebih sedikit saat di grup
  47.  
  48.  
  49. -- penggunaan lebih cepet ~50%
  50. SELECT COUNT(*)
  51. FROM   emp;
  52. --dari
  53. SELECT COUNT(empno)
  54. FROM   emp;
');