对于学生信息表：student(sno，sname，sex，age，grade)，查询学习成绩为空的学生的学号和姓名，下面语句正确的是

A:SELECT sno，sname FROM student WHERE grade=NULL B:SELECT sno，sname FROM student WHERE grade IS NULL C:SELECT sno，age FROM student WHERE grade IS NULL D:SELECT sno，age FROM student WHERE grade=NULL

学生—选课—课程数据库中的3个基本表：
学生信息表：STUDENT(sno、sname，sex，age，dept)主码为sno
课程信息表：COURSE(cno，cname，teaeher)主码为cno
学生选课信息表：SC(sno，con，grade)主码为(sno，cno)
查询“没有学习成绩的学生的学号和课程号”的SQL语句是( )。

A:SELECT sno，cno FROM SC WHERE grade=NULI 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="

对于数据表：student(sno,sname,sex,age,grade)，查询学习成绩为空的学生的学号和姓名，下面语句正确的是______。

A:SELECT sno,sname FROM student WHERE grade=NULL B:SELECT sno,sname FROM student WHERE grade IS NULL C:SELECT sno,age FROM student WHERE grade IS NULL D:SELECT sno,age FROM student WHERE grade=NULL

对于学生信息表：student(sno，sname，sex，age，grade)，查询学习成绩为空的学生的学号和姓名，下面语句正确的是( )。

A:SELECT Sno，sname FROM student WHERE grade=NULL B:SELECT sno，sname FROM student WHERE grade IS NULL C:SELECT sno，age FROM student WHERE grade IS NULL D:SELECT sno，age FROM student WHERE grade=NULL

设有一个数据库，包括S、P、J、SJP四个关系模式如下：供应商关系模式S(SNO，SNAME, CITY)零件关系模式P(PNO, PNAME, COLOR, WEIGHT)工程项目关系模式J(JNO, JNAME, CITY)供应情况关系模式SJP(SNO, PNO, JNO, QTY)假定它们都已经有若干数据。则“找出北京供应商供应的所有零件信息”的SELECT语句是( )。

A:SELECT * FROM S WHERE CITY=′北京′ B:SELECT SNO, SNAME FROM S WHERE CITY=′北京′ C:SELECT * FROM S, P WHERE CITY=′北京′AND SNO=SJ SNO AND SJ PNO= PNO D:SELECT * FROM P，S, SJP WHERE CITY=′北京′AND SNO=SJ SNO AND SJ PNO= PNO

对于数据表：student(sno,sname,sex,age,grade)，查询学习成绩为空的学生的学号和姓名，下面语句正确的是______。

A:SELECT sno,sname FROM student WHERE grade=NULL B:SELECT sno,sname FROM student WHERE grade IS NULL C:SELECT sno,age FROM student WHERE grade IS NULL D:SELECT sno,age FROM student WHERE grade=NULL

对于学生信息表：student(sno，sname，sex，age，grade)，查询学习成绩为空的学生的学号和姓名，下面语句正确的是( )。

A:SELECT Sno，sname FROM student WHERE grade=NULL B:SELECT sno，sname FROM student WHERE grade IS NULL C:SELECT sno，age FROM student WHERE grade IS NULL D:SELECT sno，age FROM student WHERE grade=NULL