What is the difference between LAG and LEAD functions?
💡 Model Answer
Both LAG and LEAD are analytic (window) functions that return a value from a row that is a specified offset away from the current row within the same partition. LAG returns a value from a preceding row (offset < 0), while LEAD returns a value from a following row (offset > 0). For example, in a sales table ordered by date, LAG(sales) gives the previous day's sales, and LEAD(sales) gives the next day's sales. They are useful for calculating differences, moving averages, or comparing adjacent rows.
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