谢谢大家的支持，很快就看到你的问题已经解决了，我已经解决了上面提到的解决方案

Thank you all for supproty see you soon my problem was solved it from myself already solution mentioned above

如果你想避免空值，请尝试如下

try like below if you want to avoid null values

DataTable dt = new DataTable();
                    dt = FnTableIDInsert();
                    foreach (DataRow dr in dt.Rows)
                    {
                        string value = dr["tableid"].ToString();
                       if(value!=null && value!=string.Empty )
                       {
                        SqlConnection connn = new SqlConnection(ConnectionString);
                        connn.Open();
                        string sqlselect = "INSERT INTO tbl_clientcolumnnames(tableid) values("+value+")";
                        SqlCommand cmdselect = new SqlCommand(sqlselect, connn);
                        cmdselect.ExecuteNonQuery();
                        string sqlselect2 = "INSERT INTO tbl_Intellectcolumnnames(tableid) values(" + value + ")";
                        SqlCommand cmdselect2 = new SqlCommand(sqlselect2, connn);
                        cmdselect2.ExecuteNonQuery();
 
                        }
                   }