DECODE KULLANARAK HIZLI ÇALIŞAN KOD YAZMAK

-- asagidaki sorgular yavas çalisacaktir.
--
-- sorgu 1
SELECT COUNT (*), SUM (sal)
FROM emp
WHERE deptno = 10 AND ename LIKE 'SMITH%';
-------------------------------
--sorgu 2
-------------------------------
SELECT COUNT (*), SUM (sal)
FROM emp
WHERE deptno = 30 AND ename LIKE 'SMITH%';
-------------------------------
-- Ayni islem için DECODE kullanarak daha hizli sonuç olariz.
--
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SELECT COUNT (DECODE (deptno, 10, '*', NULL)) d10_count,
COUNT (DECODE (deptno, 30, '*', NULL)) d30_count,
SUM (DECODE (deptno, 10, sal, NULL)) d10_sal,
SUM (DECODE (deptno, 30, sal, NULL)) d30_sal
FROM emp
WHERE ename LIKE 'SMITH%';