orcle 数据库

selectt.employeeid,t.empfirstname,t.emplastnamefromemployeest（下划线不能掉）selectt.employeeid,lower(t.empfirstname),t.emplastnamefromemployeestselectt.employeeid,t.empfirstname,t.emplastnamefromemployeestwheret.empfirstname='ann'为什么查询不到