var reader = cmd.ExecuteReader();var columns = new List<string>();for(int i=0;i<reader.FieldCount;i++){ columns.Add(reader.GetName(i));}要么
var columns = Enumerable.Range(0, reader.FieldCount).Select(reader.GetName).ToList();

var reader = cmd.ExecuteReader();var columns = new List<string>();for(int i=0;i<reader.FieldCount;i++){ columns.Add(reader.GetName(i));}要么
var columns = Enumerable.Range(0, reader.FieldCount).Select(reader.GetName).ToList();