Get affected rows on ExecuteNonQuery

ExecuteNonQuery - returns the number of rows affected.

SqlCommand comm;
// other codes
int numberOfRecords = comm.ExecuteNonQuery();

If you run the SQL from your question in a SqlCommand and check the return value of ExecuteNonQuery it should tell you how many records were affected.

From the documentation:

Return Value
Type: System.Int32
The number of rows affected.

Be sure of one thing also You need to add a statement in the connection string For example:

string const "Server=localhost; PORT=3306; Database=db; User id=root; password='';UseAffectedRows=True";
MySqlConnection con = new MySqlConnection(const);
con.Open();
MySqlCommand cmd = new MySqlCommand(con);
cmd.CommandText = "Update db set table = value where Column = value";
int numberOfRecords = cmd.ExecuteNonQuery();

Be sure of:

UseAffectedRows=True

so it will return a right value of rows affected