Oracle SQL "partition" Analytic Function tips Oracle Tips by Laurent Schneider

 

Laurent Schneider is considered one of the top Oracle SQL experts, and he is the author of the book "Advanced Oracle SQL Programming" by Rampant TechPress.  The following is an excerpt from the book.

PARTITION

As the aggregate functions use GROUP BY to group rows, analytic functions use PARTITION BY. 

SELECT
   ENAME,
   SAL,
   DEPTNO,
   MAX(SAL) OVER (PARTITION BY DEPTNO) MAX_SAL_DEPTNO,
   JOB,
   MAX(SAL) OVER (PARTITION BY JOB) MAX_SAL_JOB
FROM
   EMP;

ENAME             SAL     DEPTNO MAX_SAL_DEPTNO JOB       MAX_SAL_JOB
---------- ---------- ---------- -------------- --------- -----------
MILLER           1300         10           5000 CLERK            1300
KING             5000         10           5000 PRESIDENT        5000
CLARK            2450         10           5000 MANAGER          2975
SMITH             800         20           3000 CLERK            1300
SCOTT            3000         20           3000 ANALYST          3000
ADAMS            1100         20           3000 CLERK            1300
FORD             3000         20           3000 ANALYST          3000
JONES            2975         20           3000 MANAGER          2975
WARD             1250         30           2850 SALESMAN         1600
MARTIN           1250         30           2850 SALESMAN         1600
TURNER           1500         30           2850 SALESMAN         1600
ALLEN            1600         30           2850 SALESMAN         1600
JAMES             950         30           2850 CLERK            1300
BLAKE            2850         30           2850 MANAGER          2975

Miller is the clerk of department 10. In his department, the best paid employee has a salary of 5000. Over all clerks, his salary of 1300 is the highest.  The PARTITION BY reduces the scope to the current partition.