现有表Employee,字段:id(int),firstname(varchar),lastname(varchar);以下sql语句正确是哪三项?()
A.selectfirstname+'.'+lastnameas'name'fromemployee
B.selectfirstname+'.'+lastname='name'fromemployee
C.select'name'=firstname+'.'+lastnamefromemployee
D.selectfirstname,lastnamefromemployee