问题
单项选择题
查询选修了课程号为'C2'的学生号和姓名，若用下列SQL的SELECT语句表达时，哪一个是错误的？
A．SELECT S#，SNAME FROM S WHERE S# = (SELECT SS# FROM SC WHERE C# = 'C2' )
B．SELECT S#，SNAME FROM S，SCWHERE S# = SS# AND C# = 'C2'
C．SELECT S#，SNAME FROM S，SC WHERE S# = SS# AND C# = 'C2' ORDER BY S#
D．SELECT S#，SNAME FROM S WHERE S# IN (SELECT SS# FROM SC WHERE C# ='C2' )
答案
参考答案：A
解析：【解析】在嵌套查询中，内层查询的结果有多个，不能用“=”做条件，而应使用“in”子句。