LAG function Oracle

LAG function used to find previous row value within the same table. It is an example of analytical function.

Syntax :-

LAG(column, context, default) over partition clause

context – number of rows to go backward. Default is 1

default – default value returns. Default is null

Examples :-

Consider the emp table and below rows

SQL >  select empno,salary,lag(salary,1,0) over ( order by salary) as lag_salary
from emp;

For each row LAG function tries to find the previous row value.

lag(salary,2,0) over ( order by salary) will find the value prior 2 rows.

SQL >  select empno,salary,lag(salary,2,0) over ( order by salary) as lag_salary
from emp ;

Also read about LEAD function.