Which T-SQL clause is used with the GROUP BY clause to filter aggregate results?

The T-SQL clause used with the GROUP BY clause to filter aggregate results is the HAVING clause.

Explanation:

1. Purpose: While the GROUP BY clause is utilized to group rows that have the same values in specified columns into summary rows, the HAVING clause is employed to filter these grouped records based on a specified condition.

2. Functionality: The HAVING clause works similarly to the WHERE clause, but instead of filtering rows before grouping, it filters groups after the aggregation has been performed. This means that you can apply aggregate functions (like COUNT, SUM, AVG, etc.) within the HAVING clause to impose conditions on the aggregated output.

3. Example: If you wanted to find all departments in a company that have more than 10 employees, you might write a query like this:

   SELECT DepartmentId, COUNT(EmployeeId) AS EmployeeCount
   FROM Employees
   GROUP BY DepartmentId
   HAVING COUNT(EmployeeId) > 10;
   

In this example, the GROUP BY clause groups employees by department, and the HAVING clause filters to include only those groups with more than 10 employees.