Thread

Re: [HACKERS] Re: [GENERAL] Update of bitmask type

Jose Soares <jose@sferacarta.com> — 1999-09-24T13:01:19Z

Adriaan Joubert ha scritto:

> Hannu Krosing wrote:
> >
> > Adriaan Joubert wrote:
> > >
> > > b) seems to imply, rather bizarrely in my opinion, that
> > >
> > >         B'001100' < B'10'
> > >
> > Maybe you start counting from the wrong end ?
> >
> > Just use them as you use char()
> >
> > 'AABBAA' < 'BA'
> >
> > Does it say something in the standard about direction,
> > is it left-> right or right->left ?
>
> No, not that I could find. But in the above example B'001100' < B'10'
> whichever end you start counting from, as 1>0. I have no particularly
> strong opinion on which way round it should be done -- perhaps we should
> just try to be consistent with other databases? Could somebody who has
> access to Oracle or Sybase please do a few tests and let me know?
>

Oracle doesn't have this data type neither Informix. I think it is hard to
find this data type in any database.
I found this feature in the OCELOT database
You can download it from:
http://ourworld.compuserve.com/homepages/OCELOTSQL/
As they say:
"Ocelot makes the only Database Management System (DBMS) that supports the
full ANSI / ISO
SQL Standard (1992), and an always-growing checklist of SQL3 features (also
known as SQL-99)."



A second problem I encountered last night is that the postgres variable

> length types only allow for the length of an array to be stored in
> bytes. This means that the number of bits will automatically always be
> rounded up to the nearest factor of 8, i.e. you want tp store 3 bits and
> you get 8. For ordering and output this is not always going to produce
> the correct output, as the bitstrings will get zero-padded. Is there
> anywhere else where one could store the exact length of a bit string?
>
>  I haven't quite understood what the variable attypmod is. In varchar.c
> it looks as if it is the length of the record, but if it is just an
> integer identifier, then I could store the exact length in there. In
> that case I could handle the difference between 3 and 5 bit strings
> correctly. My main worry was that this might be used in other routines
> to determine the length of a record.
>
> Adriaan
>
> ************