C# 使用DataSet得不到数据
sql语句为：ELECT   TOP (4) CarImagePart.carImageName, CarImagePart.carTypeId, CarImage.carImageKindName  " +
                          "FROM      CarImagePart INNER JOIN   " +
                          " CarImage ON CarImagePart.carImagePartId = CarImage.carImagePartId  " +
                         "WHERE   (CarImagePart.carTypeId = " + Convert.ToInt32(carTypeId)
                         +" )"

在数据库中新建查询时能够查到数据，但是用下面的方法返回的DataSet却为空，这是怎么回事啊？

 public static DataSet getDataSet(string sql)
        {
           
            using (SqlConnection conn = new SqlConnection(connStr))
            {
                using (SqlDataAdapter adapter = new SqlDataAdapter(sql, conn))
                {
                    try
                    {
                        DataSet ds = new DataSet();
                        adapter.Fill(ds);
                        return ds;
                    }
                    catch
                    {
                        return null;
                     }
                }
            }
         }