16. How does ORDER BY work

• MySQL has three sort modes:
  • <sort_key, rowid>: sort buffer only contains the row_id and does not contain the actual row
  • <sort_key, additional_fields>: sort buffer contains all columns referenced by the query
  • <sort_key, packed_additional_fields>: sort buffer contains packed version of all columns (use actual length rather than fixed-length encoding)
• See https://dev.mysql.com/doc/refman/8.0/en/order-by-optimization.html