大家帮我解释一下一个sql语句
sql = "Select Top 30 " sql = sql & "d.id,d.SoftName,d.CreateTime,d.TotalHits,d.ClassId,c.ClassName,c1.ClassName AS nCName "
sql = sql & " From DownLoad d,Class c,Class c1 Where d.IsHide=0 And d.ClassId=c1.ClassId And c.ClassId=c1.UpperId"
sql = sql & " Order By d.CreateTime Desc"