Window functions are where analytics gets powerful without messy joins. Lead and lag are two of the most practical tools: they let you “peek” into the next or previous row to compare, detect changes, ...

You don’t just need the current value. You need to know what changed. LAG() is used to compare each row to the one before it. It lets you look at the previous row without joins or subqueries. The ...

I want to design a query to compute some returns for stock data and in searching the 'SQL Server Books Online' I find a very small and not so helpful at all help section on the lead and lag functions.

SELECT e.*, LAG(salary) over(partition by dept_name ORDER BY emp_id) AS Pre_Employee_Sal, LEAD(salary) over(partition by dept_name ORDER BY emp_id) AS Next_Employee ...