DOM--sql server

 1    public List<LianHeData> select(int ID)
 2         {
 3             List<LianHeData> list = new List<LianHeData>();
 4             conn.Open();
 5             cmd = conn.CreateCommand();
 6                 //*************************************************************************************************
 7             cmd.CommandText = "select a.Name name1,b.Name name2,c.Name name3 from Users a,Nation b,Clas c where a.ClassCode=b.Code and a.NationCode=c.Code and a.ID=@ID";
                          //**********************************************************************************************
 8             cmd.Parameters.Clear();            
 9             //放入到缓存中
10             cmd.Parameters.Add("@ID", ID);
11             SqlDataReader dr = cmd.ExecuteReader();
12 
13             while (dr.Read())
14             {
15                 LianHeData data = new LianHeData();
16                 data.Name11 = dr["name1"].ToString();
17                 data.Name21 = dr["name2"].ToString();
18                 data.Name31 = dr["name3"].ToString();
19                 //data.ID1 = int.Parse(dr["ID"].ToString());
20                 //data.Name1 = dr["Name"].ToString();
21                 //data.PWD1 = dr["PWD"].ToString();
22                 //data.QuanXian1 = int.Parse(dr["QuanXian"].ToString());
23                 //data.NationCode1 = int.Parse(dr["NationCode"].ToString());
24                 //data.ClassCode1 = int.Parse(dr["ClassCode"].ToString());
25                 list.Add(data);
26               
27             }
28             return list;
29            
30         }

"select a.Name,b.Name,c.Name from Users a,Nation b,Clas c where a.ClassCode=b.Code and a.NationCode=c.Code and a.ID=@ID"是查不出数据的

必须定一个定量“select a.Name name1,b.Name name2,c.Name name3 from Users a,Nation b,Clas c where a.ClassCode=b.Code and a.NationCode=c.Code and a.ID=@ID”