(1)检索年龄大于23岁的女生的学号和姓名。(2)检索选修课程包含LIU老师所授课程的学生学号及姓名。(3)检索选修课程号为C1和C4的学生学号。(4)检索学习全部课程的学生姓名
.(1)πS#,SNAME(σAGE>23∧SEX=′F′(S)) SELECT S#，SNAME FROM S WHERE AGE>23 AND SEX=′F′ (2)πS#,SNAME(σTEACHER=′LIU′(S??SC??C)) SELECT S#,SNAME FROM S WHERE EXISTS (SELECT * FROM SC WHERE EXISTS (SELECT * FROM C WHERE S.S#=SC.S# AND SC.C#=C.C# AND TEACHER=′LIU′)); (3)πS#(σC#=′C1′∧ ′C#=′C4′(′SC)) SELECT SC WHERE C#=′C1′ AND C#=′C4′; (4)πSNAME(S??(πS#,C#(SC)÷πC#(C))) SELCET SNAME FROM S WHERE NOT EXISTS (SELECT * FROM C WHERE NOT EXISTS (SELECT * FROM SC WHERE SC.S#=S.S# AND C.C#=SC.C#)) 试用SQL查询语句表达下列对教学数据库中三个基本表S、SC、C的查询：
