I'm really perplexed that people find these names so confusing. seleactall_arrayref *selects* *all* rows returned into an *array* *ref*erence. selectall_hashref *selects* *all* rows returned into a *hash* *ref*. The confusion comes because there are two types of arrayrefs in Perl - a reference to an Array of Array refs (AoA) and a reference to an Array of Hash references (AoH). DBI disambiguates them by allowing you to supply a slice as an argument to the arrayref and therefore specifying that you want an AoH instead of an AoA. In either case you are getting back a reference to an array and therefore want selectall_arrayref.

If my verbiage doesn't clarify, perhaps these succinct examples will help.

update You might want to check out the latest DBI since the docs you cite have been rewritten and are perhaps clearer (if not, submit a doc patch). One thing that the newer docs make clear is that the attributes hash in select_all_arrayref($stmt, \%attr, @vals) is a very powerful feature and that supplying a slice is only one of the things you can do with it. If you supply a max value in the attributes hash, for example, your result set will be limited to that number of rows (a perl version of LIMIT for those databases that don't support it.

The basic idea is that the name of the method "selectall_arrayref" specifies what kind of a strucure the results will be returned in and the attributes hash specifies the characteristics of that structure. Yes, I do see how that can be a bit confusing, but it's also a very powerful concept. Upcoming versions of DBI will use these attribute hashes to methods even more extensively allowing you to specify both the return structure, attributes of that structure, and attributes of the method of fetching.

update 2 Thanks for bringing this up, it's forced me to think :-). Here's a generic description of a DBI method call that applies to selectall_arrayref and most other DBI methods: 
$handle->what_perl_structure_to_fetch_results_into(
   $what_results_to_fetch,
   \%characteristics_of_the_fetch_and_of_the_fetch_into,
   @values_to_further_specify_what_to_fetch

);

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In reply to Re^2: Weird DBI behaviour by jZed
in thread Weird DBI behaviour by toadi

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