What is a Window Function?

Concepts: sqlPartitionBy

What Window Functions Solve Consider a common analytical question: "Show me each employee's salary alongside the average salary for their department." This requires two things at once: individual row detail (each employee's name and salary) and aggregate context (the department average). Before window functions existed, you had to write a subquery or a self-join to combine these. Window functions let you do it in a single, clean pass. Comparing Approaches Here is our employee data: GROUP BY Result (Collapsed) Only three rows remain. All employee-level detail is gone. You cannot tell who earns what. Preserved Rows in Results The OVER Clause