求助：聚合函数SUM的用法。谢谢！
USE masterGO
--检验数据库是否存在，如果为真，删除此数据库--
IF exists(SELECT * FROM sysdatabases WHERE name='Student')
DROP DATABASE Student
GO
CREATE DATABASE Student
GO
--建数据表--
USE Student
GO
CREATE TABLE Member --学生表
(
MID char(10) primary key, --学生号
MName CHAR(50) NOT NULL --姓名
)
GO
CREATE TABLE F --课程表
(
FID char(10) primary key, --课程号
FName CHAR(50) NOT NULL --课程名
)
GO
CREATE TABLE score --学生成绩表
(
SID int identity(1,1) primary key, --成绩记录号
FID char(10) foreign key(FID) references F(FID) , --课程号
MID char(10) foreign key(MID) references Member(MID) , --学生号
Score int NOT NULL --成绩
)
GO
--课程表中插入数据--
INSERT INTO F(FID,FName)VALUES('F001','语文')
INSERT INTO F(FID,FName)VALUES('F002','数学')
INSERT INTO F(FID,FName)VALUES('F003','英语')
INSERT INTO F(FID,FName)VALUES('F004','历史')
--学生表中插入数据--
INSERT INTO Member(MID,MName)VALUES('M001','张萨')
INSERT INTO Member(MID,MName)VALUES('M002','王强')
INSERT INTO Member(MID,MName)VALUES('M003','李三')
INSERT INTO Member(MID,MName)VALUES('M004','李四')
INSERT INTO Member(MID,MName)VALUES('M005','阳阳')
INSERT INTO Member(MID,MName)VALUES('M006','虎子')
INSERT INTO Member(MID,MName)VALUES('M007','夏雪')
INSERT INTO Member(MID,MName)VALUES('M008','璐璐')
INSERT INTO Member(MID,MName)VALUES('M009','珊珊')
INSERT INTO Member(MID,MName)VALUES('M010','香奈儿')
--成绩表中插入数据--
INSERT INTO Score(FID,MID,Score)VALUES('F001','M001',78)
INSERT INTO Score(FID,MID,Score)VALUES('F002','M001',67)
INSERT INTO Score(FID,MID,Score)VALUES('F003','M001',89)
INSERT INTO Score(FID,MID,Score)VALUES('F004','M001',76)
INSERT INTO Score(FID,MID,Score)VALUES('F001','M002',89)
INSERT INTO Score(FID,MID,Score)VALUES('F002','M002',67)
INSERT INTO Score(FID,MID,Score)VALUES('F003','M002',84)
INSERT INTO Score(FID,MID,Score)VALUES('F004','M002',96)
INSERT INTO Score(FID,MID,Score)VALUES('F001','M003',70)
INSERT INTO Score(FID,MID,Score)VALUES('F002','M003',87)
INSERT INTO Score(FID,MID,Score)VALUES('F003','M003',92)
INSERT INTO Score(FID,MID,Score)VALUES('F004','M003',56)
INSERT INTO Score(FID,MID,Score)VALUES('F001','M004',80)
INSERT INTO Score(FID,MID,Score)VALUES('F002','M004',78)
INSERT INTO Score(FID,MID,Score)VALUES('F003','M004',97)
INSERT INTO Score(FID,MID,Score)VALUES('F004','M004',66)
INSERT INTO Score(FID,MID,Score)VALUES('F001','M006',88)
INSERT INTO Score(FID,MID,Score)VALUES('F002','M006',55)
INSERT INTO Score(FID,MID,Score)VALUES('F003','M006',86)
INSERT INTO Score(FID,MID,Score)VALUES('F004','M006',79)
INSERT INTO Score(FID,MID,Score)VALUES('F002','M007',77)
INSERT INTO Score(FID,MID,Score)VALUES('F003','M008',65)
INSERT INTO Score(FID,MID,Score)VALUES('F004','M007',48)
INSERT INTO Score(FID,MID,Score)VALUES('F004','M009',75)
INSERT INTO Score(FID,MID,Score)VALUES('F002','M009',88)
-- 1)查询各个学生语文、数学、英语、历史课程成绩--
SELECT Member.MName AS 姓名,
语文 = SUM(CASE F.FName WHEN '语文' THEN Score.Score END),
数学 = SUM(CASE F.FName WHEN '数学' THEN Score.Score END),
语文 = SUM(CASE F.FName WHEN '英语' THEN Score.Score END),
历史 = SUM(CASE F.FName WHEN '历史' THEN Score.Score END)
FROM Score, Member,F
WHERE F.FID = Score.FID AND Member.MID =Score.MID GROUP BY Member.MName
求助：请问此处sum的具体含义，谢谢
-- 2)查询四门课中成绩低于70分的学生及相对应课程名和成绩--
select 姓名=(select MName from Member where MID=Score.MID),课程名=(select FName from F where FID=Score.FID),成绩=Score from Score where Score<70
-- 3)统计各个学生四课程的平均分，且按平均分数由高到底排序--
select 姓名=(select MName from Member where MID=Score.MID),平均分=Avg(Score) from Score group by MID order by 平均分 desc
-- 4)创建存储过程--
if exists (select * from sysobjects where name='P_stu')
drop procedure P_stu
GO
create procedure P_stu
@num int
As
print'参加'+convert(varchar(5),@num)+'门课考试的学生姓名及学号：'
select 姓名=(select MName from Member where MID=Score.MID),学号=MID from Score group by MID having count(*)=@num
--调用存储过程--
exec P_stu @num=2
