Write a query to unpivot columns into rows.

Short answer: Use UNPIVOT or CROSS APPLY (VALUES ...) to turn columns into attribute/value rows — handy for EAV-style reporting.

Sample solution

SELECT EmpId, Metric, Val
FROM EmployeesWide
CROSS APPLY (VALUES
    ('Salary', Salary),
    ('Bonus', Bonus),
    ('Allowance', Allowance)
) v(Metric, Val);

VALUES unpivot is often clearer than the UNPIVOT operator.