/*30、查询同名同姓学生名单，并统计同名人数*/

Select Sname,count(*) as NUM from Student

group by Sname having count(*)>1

/*30、查询同名同性学生名单，并统计同名男生人数*/

Select Sname,Ssex,count(*) as num from Student

group by Sname,Ssex having count(*)>1 and Ssex='男'

\*39求选了课程的学生人数 *\

select COUNT(*), s.Sname from Student s, SC c where s.S# = c.S#

select  COUNT(distinct S#) from SC;

/*计算每个学生选了什么课程*/

select count(aa.S#) , aa.C# from (select SC1.S#, SC1.C# from SC SC1 where SC1.S# in

(select SC2.S# from SC SC2 group by SC2.S#))  as aa group by aa.S#,aa.C#

select S#,C# from SC SC2 group by S#,C#

select count(s.Sname) from Student s where s.S# in (select distinct c.S# from SC c)

select count(distinct s.Sname) from Student s;

\*39求选了(不同)课程的学生人数 *\

select C#, count(distinct S#) from SC group by C# order by C#

select COUNT(distinct S#) from SC where C#=23;

select * from SC c where c.S#=1;

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