查询姓张、姓王、姓刘老师的信息的方法是
A. SELECT *FROM TeacherWHERE Teachername like '张%' and Teachername like '王%' and Teachername like '刘%'
B. SELECT *FROM TeacherWHERE Teachername like '张%' or Teachername like '王%' and Teachername like '刘%'
C. SELECT *FROM TeacherWHERE Teachername like '张%' or Teachername like '王%' or Teachername like '刘%'
D. SELECT *FROM TeacherWHERE Teachername like '张%' and Teachername like '王%' or Teachername like '刘%'
返回组中值的平均值,使用( )函数
A. count
B. sum
C. avg
D. min
除count函数外,聚合函数一般忽略空值,且仅用于()
A. 日期型列
B. 字符型列
C. 数值型列
D. 二进制列
返回表中项目的数量,应使用()函数
A. sum
B. avg
C. max
D. count