已知有学生关系S(SNO,SNAME,AGE,DNO),各属性含义依次为学号,姓名、年龄和所在系号;学生选课关系SC(SNO,CNO,SCORE),各属性含义依次为学号、课程号和成绩。分析以下SQL语句:SELECT SNO FROM SC WHERE SCORE = (SELECT MAX(SCORE) FROM SC WHERE CNO=’002’) 简述上述语句完成的查询操作是
举一反三
- 查询选课关系SC(Sno,Cno,Score)表中还没有给定成绩()的课程号()和学号(),下列语句正确的是。() A: SELECT<br/>Sno,Cno<br/>FROM SC WHERE Score IS NULL B: SELECT*<br/>FROM SC WHERE Score =NULL C: SELECT<br/>Sno,Cno<br/>FROM SC D: SELECT<br/>Score FROM SC WHERE Sno,Cno<br/>IS NOT NULL
- 有关系S(SNO, SNAME, SAGE),C(CNO, CNAME),SC(SNO, CNO, GRADE)。其中SNO是学生号,SNAME是学生姓名,SAGE是学生年龄, CNO是课程号,CNAME是课程名称,GRADE是成绩。以下( )SQL语句可以实现查询选修了'C002'号课程的学生姓名。 A: SELECT SNAME FROM S, SC WHERE S.SNO=SC.SNO AND CNO='C002' B: SELECT SNAME FROM S WHERE SNO IN (SELECT SNO FROM SC WHERE CNO='C002') C: SELECT SNAME FROM S WHERE SNO = (SELECT SNO FROM SC WHERE CNO='C002') D: SELECT SNAME FROM S WHERE SNO NOT IN (SELECT SNO FROM SC WHERE CNO='C002')
- 查询所有有成绩的学生学号和课程号。正确的SELECT语句是()。 A: Select sno , cno from sc where grade < > null B: Select sno as 学号, cno as 课程号 from sc where grade is not null C: Select sno , cno from sc where grade !=‘ ’ D: Select sno , cno from sc where grade is not null
- 已知学生选课信息表sc(sno, cno, degree)。查询“至少选修了一门课程,但没有成绩的学生学号和课程号”的SQL语句是( )。 A: SELECT sno, cno FROM sc WHERE degree=NULL; B: SELECT sno, cno FROM sc WHERE degree IS ''; C: SELECT sno, cno FROM sc WHERE degree IS NULL; D: SELECT sno, cno FROM sc WHERE degree='';
- 已知学生选课信息表:sc(sno,cno,grade)。查询“至少选修了一门课程,但没有学习成绩的学生学号和课程号”的SQL语句是( )。 A: SELECT sno,cno FROM sc WHERE grade=NULL B: SELECT sno,cno FROM sc WHERE grade IS C: SELECT sno,cno FROM sc WHERE grade IS NULL D: SELECT sno,cno FROM sc WHERE grade=