oracle 分析函数lag lead

LAG

is an analytic function. It provides access to more than one row of a table at the same time without a self join. Given a series of rows returned from a query and a position of the cursor,

LAG

provides access to a row at a given physical offset prior to that position.

For the optional

offset

argument, specify an integer that is greater than zero. If you do not specify

offset

, then its default is 1. The optional

default

value is returned if the offset goes beyond the scope of the window. If you do not specify

default

, then its default is null.

{

RESPECT

|

IGNORE

}

NULLS

determines whether null values of

value_expr

are included in or eliminated from the calculation. The default is

RESPECT

NULLS

.

You cannot nest analytic functions by using

LAG

or any other analytic function for

value_expr

. However, you can use other built-in function expressions for

value_expr

.

比如有这样一个需求，按员工号排序。显示每个员工的sal的上一个sal是多少。

SELECT empno,ename, sal, LAG(sal,1,sal) over(ORDER BY empno)AS lastone FROM emp

结果如图

1 7369 SMITH 800.00 800
2 7499 ALLEN 1600.00 800
3 7521 WARD 1250.00 1600
4 7566 JONES 2975.00 1250
5 7654 MARTIN 1250.00 2975
6 7698 BLAKE 2850.00 1250
7 7782 CLARK 2450.00 2850
8 7788 SCOTT 3000.00 2450
9 7839 KING 5000.00 3000
10 7844 TURNER 1500.00 5000
11 7876 ADAMS 1100.00 1500
12 7900 JAMES 950.00 1100
13 7902 FORD 3000.00 950
14 7934 MILLER 1300.00 3000

lead则为下一个，如lag