设学生选课关系模式为SC(Sno,Cno,Grade),其中,Sno为,Cno为课程号, Grade为成绩,SQL查询语句如下: SELECT Sno FROMSC SCX WHERE NOT EXISTS (SELECT* FROM SC SCY WHERE SCY.Sno='1042'AND NOT EXISTS (SELECT * FROMSCSCZ WHERE SCZ.Sno=SCX.Sno AND SCZ.Cno=SCY.Cno));与该查询等价的元组演算表为{t|(13)(SC(u)∧SC(v)∧(14)∧t[1]= u[1])}。