Get affected rows on ExecuteNonQuery

ExecuteNonQuery - returns the number of rows affected.

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

ExecuteNonQuery return the affected rows ONLY WHEN Use Affected Rows in the connections properties is set, if not (default) returns matched rows.

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

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.