Question

I’m using Visual C# 2010 express windows form application & Mysql for DB.
I want to get a value (current no of students) from DB and increase it by 1 and update that value. for that I use the below code, but I’m getting an error called “unknown column ‘x’ in ‘field list’.

    connection.Open();
    MySqlCommand cmd1 = new MySqlCommand("SELECT NoOfStudents FROM batch", connection);
                MySqlDataReader dr = null;
                dr = cmd1.ExecuteReader();
                int x;
                while (dr.Read())
                {
                x = Convert.ToInt32(dr[0]);
                x = x + 1;
               }
                dr.Close();
                MySqlCommand cmd2 = new MySqlCommand("UPDATE batch SET NoOfStudents= x", connection);
                cmd2.ExecuteNonQuery();
                connection.Close();

Answer 1

try this

string sql=string.Format("UPDATE batch SET NoOfStudents= {0}",x);
MySqlCommand cmd2 = new MySqlCommand(sql, connection);

x is a variable declared in your program and Mysql dont know any thing about it, this is just a string and its content is ignored by the compiler