LAG and LEAD FUNCTIONS IN SQL

LAG:

   

 SELECT empno,
         ename,
         job,
         sal,
         LAG(sal, 1, 0) OVER (ORDER BY sal) AS sal_prev,
         sal - LAG(sal, 1, 0) OVER (ORDER BY sal) AS sal_diff 

 FROM   emp;

LEAD:

 SELECT empno,
         ename,
         job,
         sal,
         LEAD(sal, 1, 0) OVER (ORDER BY sal) AS sal_next,
         LEAD(sal, 1, 0) OVER (ORDER BY sal) - sal AS sal_diff
 FROM   emp;