Man pages matching name jifty::dbi::collection::union in section 3pm:

Jifty::DBI::Collection::Union.3pm.en	debian 10 / libjifty-dbi-perl
Jifty::DBI::Collection::Union.3pm.en	debian 11 / libjifty-dbi-perl
Jifty::DBI::Collection::Union.3pm.en	debian 12 / libjifty-dbi-perl