When filed is an INT (data type), what should I choose as sorting in MySQL?
Sorting affects row sorting. This does not affect numeric data types.
This may, however, affect how the numbers embedded in strings are sorted. But this still does not affect numeric data types such as INT.
As far as I know, you can specify sorting (or a character set) only for string types, i.e. types VARCHAR, CHAR, ENUM, SET and TEXT (TINYTEXT, TEXT, MEDIUMTEXT, LONGTEXT)