oracle求同比,环比函数(LAG与LEAD)的详解

Lag和Lead函数可以在一次查询中取出同一字段的前N行的数据和后N行的值。这种操作可以使用对相同表的表连接来实现，不过使用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 -- 环比分析，与上个月份进行比较 
 ,LAG(SALARY, 12, 0) OVER(PARTITION BY EMPLOYEENO ORDER BY YEARMONTH) AS PREV_12_SAL -- 同比分析，与上个年度相同月份进行比较 
 ,SUM(SALARY) OVER(PARTITION BY EMPLOYEENO, SUBSTR(YEARMONTH, 1, 4) ORDER BY YEARMONTH RANGE UNBOUNDED PRECEDING) LJ --累计值
 FROM SALARYBYMONTH
ORDER BY EMPLOYEENO
 ,YEARMONTH

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