Lag和Lead函數(shù)可以在一次查詢中取出同一字段的前N行的數(shù)據(jù)和后N行的值。這種操作可以使用對相同表的表連接來實現(xiàn)，不過使用LAG和LEAD有更高的效率。
CREATE TABLE salaryByMonth
(
employeeNo varchar2(20),
yearMonth varchar2(6),
salary number
) ;
insert into SALARYBYMONTH (EMPLOYEENO, YEARMONTH, SALARY)
values (1, '200805', 500);
insert into SALARYBYMONTH (EMPLOYEENO, YEARMONTH, SALARY)
values (1, '200802', 150);
insert into SALARYBYMONTH (EMPLOYEENO, YEARMONTH, SALARY)
values (1, '200803', 200);
insert into SALARYBYMONTH (EMPLOYEENO, YEARMONTH, SALARY)
values (1, '200804', 300);
insert into SALARYBYMONTH (EMPLOYEENO, YEARMONTH, SALARY)
values (1, '200708', 100);
commit;
SELECT EMPLOYEENO
,YEARMONTH
,SALARY
,MIN(SALARY) KEEP(DENSE_RANK FIRST ORDER BY YEARMONTH) OVER(PARTITION BY EMPLOYEENO) FIRST_SALARY -- 基比分析 salary/first_salary
,LAG(SALARY, 1, 0) OVER(PARTITION BY EMPLOYEENO ORDER BY YEARMONTH) AS PREV_SAL -- 環(huán)比分析，與上個月份進行比較
,LAG(SALARY, 12, 0) OVER(PARTITION BY EMPLOYEENO ORDER BY YEARMONTH) AS PREV_12_SAL -- 同比分析，與上個年度相同月份進行比較
,SUM(SALARY) OVER(PARTITION BY EMPLOYEENO, SUBSTR(YEARMONTH, 1, 4) ORDER BY YEARMONTH RANGE UNBOUNDED PRECEDING) LJ --累計值
FROM SALARYBYMONTH
ORDER BY EMPLOYEENO
,YEARMONTH
