4.分组、排序和输出行

SELECT Sex,COUNT(Sex)
  FROM employees
    GROUP BY Sex;
SELECT DepartmentName,COUNT(DepartmentName) AS 人数
  FROM departments LEFT OUTER JOIN employees
    ON departments.DepartmentID=employees.DepartmentID
    GROUP BY DepartmentName;
 SELECT Education,COUNT(Education) AS 人数
  FROM employees
    GROUP BY Education;
SELECT WorkYear as 工作年份,COUNT(*) AS 人数
  FROM employees
    GROUP BY WorkYear
    ORDER BY WorkYear;