使用ExecuteScalar执行聚合函数查询返回值总是0的问题

 1 　　　　public int CheckUserName(string username) 
 2 { 
 3 DBClass db = new DBClass(); 
 4 int a; 
 5 using (SqlConnection conn = db.GetConn()) 
 6 { 
 7 SqlCommand cmd = new SqlCommand("select count(*) from tb_Member111 where id = '" + username + "'", conn); 
 8 a = Convert.ToInt32(cmd.ExecuteScalar()); 
 9 conn.Close(); //关闭后再返回，否则返回值永远是0
10 return a; 
11 } 
12 }

把SqlConnection关闭再返回才是关键！！