关联子查询
SELECT EmployeeID,Title,VacationHours FROM HumanResources.Employee E1 WHERE E1.VacationHours > (SELECT AVG(E2.VacationHours) FROM HumanResources.Employee E2 WHERE E1.Title = E2.Title) HumanResources.Employee 它们不是同一个表吗？为什么还要单独命名，求解
