Moving Average

The following query computes the moving average of the salary amount between the current department and the previous three departments: ROWS BETWEEN 3 PRECEDING AND CURRENT ROW defines the start of the window as including the three rows preceding the current row; the end of the window is the current row being processed.


CREATE TABLE EMP (EMPNO NUMBER(4) NOT NULL,
                  ENAME VARCHAR2(10),
                  JOB VARCHAR2(9),
                  SAL NUMBER(7, 2),
                  DEPTNO NUMBER(2));

INSERT INTO EMP VALUES (1, 'SMITH', 'CLERK',     800,    20);
INSERT INTO EMP VALUES (2, 'ALLEN', 'SALESMAN', 1600,    30);
INSERT INTO EMP VALUES (3, 'WARD',  'SALESMAN', 1250,    30);
INSERT INTO EMP VALUES (4, 'JONES', 'MANAGER',  2975,    20);
INSERT INTO EMP VALUES (5, 'MARTIN','SALESMAN', 1250,    30);
INSERT INTO EMP VALUES (6, 'BLAKE', 'MANAGER',  2850,    30);
INSERT INTO EMP VALUES (7, 'CLARK', 'MANAGER',  2850,    10);
INSERT INTO EMP VALUES (8, 'SCOTT', 'ANALYST',  3000,    20);
INSERT INTO EMP VALUES (9, 'KING',  'PRESIDENT',3000,    10);
INSERT INTO EMP VALUES (10,'TURNER','SALESMAN', 1500,    30);
INSERT INTO EMP VALUES (11,'ADAMS', 'CLERK',    1500,    20);

SQL> SELECT
  2  deptno, SUM(sal) AS month_amount,
  3  AVG(SUM(sal)) OVER (ORDER BY deptno ROWS BETWEEN 3 PRECEDING AND CURRENT ROW)
  4  AS moving_average
  5  FROM emp
  6  GROUP BY deptno
  7  ORDER BY deptno;

    DEPTNO MONTH_AMOUNT MOVING_AVERAGE
---------- ------------ --------------
        10         5850           5850
        20         8275         7062.5
        30         8450           7525

SQL>

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