1下列SELECT语句的作用是从学生信息表(Student_Info)中统计出家住北京市的男生和女生各自的总人数和平均年龄,阅读程序并选择正确的答案。SELECT Student_Sex AS 性别,___(14)___ AS 总人数,AVG(year(getdate())-yeay(Born_Date)) AS 平均年龄FROM Student_InfoWHERE Substring(Address,1,3)=‘北京市’__...