SQL CASE

SELECT
  FirstName, LastName,
  Salary, DOB,
  CASE Gender
    WHEN 'M' THEN 'Male'
    WHEN 'F' THEN 'Female'
  END
FROM Employees

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SELECT
  CASE 
    WHEN GROUPING(Department) = 1 THEN 'Company Average'
    ELSE Department
  END AS Department,
  AVG(Salary) as AvgSalary
FROM Employees
GROUP BY Department
WITH ROLLUP