1. DBD::mysql does not support named placeholders. 2. The current version of DBD::Pg does not support named placeholders even thought they might work. What you are seeing is some legacy code from DBD::Oracle that was left in the driver code, but it does not work as it should, and is not well tested. The next version of DBD::Pg will have full support named placeholders, however.

You can get the latest beta here: http://search.cpan.org/CPAN/authors/id/R/RU/RUDY/DBD-Pg-1.31_5.tar.gz