A.Select email from student where email!=null B.Select email from student where emailnotisnull C.Select email from student where email<>null D.Select email from student where emailisnotnull
A.LIMIT B.TOP C.COUNT D.SUM
A.select top3 cDiscription fromTvtype order by iprice asc B.select cDiscription from Tvtype where max(iprice)>3 C.select top3 cDiscription from Tvtype order by iprice desc D.selec tcDiscription max(iprice)from Tvtype order by iprice