public string CheckDataYear(string logid) 
{
  string year="";
  string connect = "User ID=appDB;Initial Catalog=appDB;Data Source=LJJ;Password=appDB123"; 
  using(SqlConnection con = new SqlConnection(connect)){ 
    con.Open(); 
    string sql= "select jyrqy from t_tzsb_ylss_ys1_new where djid='logid'"; 
    SqlCommand com = new SqlCommand(sql,con);
    SqlDataReader rd=com.ExecuteReader();
    if(rd.read()){
      year = rd["字段名"].ToString();//出错 
     }
  }
    return year; 
}

------解决方案--------------------
        string year = com.ExecuteScalar().Tostring;//出错  
是  ToString()

------解决方案--------------------
    string year = com.ExecuteScalar().Tostring;//出错  
确定这个地方返回的值不是null?


------解决方案--------------------
探讨

不过要想让连接能够即时关闭,最好使用using 
如下 

C# code
public string CheckDataYear(string logid) 
{
  string year="";
  string connect = "User ID=appDB;Initial Catalog=appDB;Data Source=LJJ;Password=appDB123"; 
  using(SqlConnection con = new SqlConnection(connect)){ 
    con.Open(); 
    string sql= "select jyrqy from t_tzsb_ylss_ys1_new where djid='logid'"; 
    SqlCommand com = n…