ExecuteNonQuery returns 1 even if update statement didn't affect any row

I am facing a quite strange problem here.

My DAL was written using OdbcConnection objects and was perfectly working.

However I had to respect some requirements and therefore had to move the system to use MySqlConnection

Shouldn't give any problem, would you say.

However, there is a little misunderstanding now: when I execute an UPDATE command, without entering any new detail (let's say I change the user "test"'s username to... "test"), the command.ExecuteNonQuery() returns 1 anyway.

With the previous system & OdbcCommand objects, it returned 0 if no field changed.

Is it just a basic difference between the two systems or is there anything I've missed here?

Just some code even if it is very basic:

private readonly string _updateUserCommand =
            "UPDATE user u " +
            "JOIN city c ON c.Name=?City " +
            "SET `City Id`=c.Id, u.Username=?Username WHERE u.Id=?Id";

// (...)

MySqlCommand command = null;
                try
                {
                    connection.Open();
                    //First step: storing the user in table user
                    //Creating the actual command:
                    command = new MySqlCommand(_updateUserCommand, connection);
                    command.Parameters.AddWithValue("?City", u.City);
                    开发者_运维问答command.Parameters.AddWithValue("?Username", u.Name);
                    command.Parameters.AddWithValue("?Id", u.Id);

                    int i = command.ExecuteNonQuery(); 
                    if (i != 0) return true;
                    else return false;
                }

Your explanation doesn't make much sense. If you give a valid id and do an update on the username even if you update to the same name you can expect that 1 row will be affected. i.e. there is one row with the userId

ExecuteNonQuery returns the number of rows it changed, even if that change isn't noticeable to a human reader. The query did find a match and it did update one row. SQL really doesn't pay that much attention to what the old value was, it simply overwrites it and counts that as one row altered.