Can there be any reason for determining FK constraints in MyISAM? MyISAM does not enforce referential integrity, right? So perhaps there's no reason to FK constraints.

Although MySQL parses and ignores them on MyISAM tables, I believe you need to write them for 3 reasons.

  • Preparation: Your code is going to be ready when MyISAM will get there.
  • Documentation: Everyone knows that which you intended. A lot better than trying to puzzle out where foreign secrets are meant to go annually from now.
  • Insurance: If MyISAM fails you, you are able to move straight to InnoDB tables.

http://dev.mysql.com/doc/refman/5.0/en/ansi-diff-foreign-keys.html

In the finish of second column:

In a later stage, foreign key constraints is going to be implemented for MyISAM tables too.

apparently in mysql 5. 'latter stage' hasn't come yet
constraints are essential being an additional validation