What is the difference between LAG() and LEAD()?

Both access values from other rows within the window without self-joins. LAG(col, n, default): returns the value from n rows BEFORE the current row within the partition. LEAD(col, n, default): returns the value from n rows AFTER the current row. Default: value returned when n goes out of partition bounds (default is NULL). Example: SELECT revenue, LAG(revenue, 1, 0) OVER (ORDER BY month_date) AS p