设有三个基本表S(S#,SNAME,AGE,SEX),SC(S#,C#,GRADE)和C(C#,CNAME,TEACHER),试用SQL查询语句表达代数表达达式.(1)πSNAME(S)(2)σAGE<20(S)(3)πSNAME(σAGE<20(S))(4)πS#,GRADE(σC#=‘C2’(SC))
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![设有三个基本表S(S#,SNAME,AGE,SEX),SC(S#,C#,GRADE)和C(C#,CNAME,TEACHER),试用SQL查询语句表达代数表达达式.(1)πSNAME(S)(2)σAGE<20(S)(3)πSNAME(σAGE<20(S))(4)πS#,GRADE(σC#=‘C2’(SC))](/uploads/image/z/5479969-49-9.jpg?t=%E8%AE%BE%E6%9C%89%E4%B8%89%E4%B8%AA%E5%9F%BA%E6%9C%AC%E8%A1%A8S%28S%23%2CSNAME%2CAGE%2CSEX%29%2CSC%28S%23%2CC%23%2CGRADE%29%E5%92%8CC%28C%23%2CCNAME%2CTEACHER%29%2C%E8%AF%95%E7%94%A8SQL%E6%9F%A5%E8%AF%A2%E8%AF%AD%E5%8F%A5%E8%A1%A8%E8%BE%BE%E4%BB%A3%E6%95%B0%E8%A1%A8%E8%BE%BE%E8%BE%BE%E5%BC%8F.%281%29%CF%80SNAME%28S%29%282%29%CF%83AGE%EF%BC%9C20%28S%29%283%29%CF%80SNAME%28%CF%83AGE%EF%BC%9C20%28S%29%29%284%29%CF%80S%23%2CGRADE%28%CF%83C%23%EF%BC%9D%E2%80%98C2%E2%80%99%28SC%29%29)
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