Re: can someone explain confusing array indexing nomenclature

Yes, it is confusing. I have an update to the array documentation that
should clarify it --- attached.

---------------------------------------------------------------------------

Achilleas Mantzios wrote:
> ???? ????????? 16 ??????????? 2007 20:35, ?/? chrisj ??????:
> > I am quite sure the [2] is not discarded, easy enough to test but I don't
> > have access to PG at the moment.
>
> Well it should, since
>
> dynacom=# SELECT
> (CAST( '{{meeting,lunch},{training,presentation}}' as text[][]))[1:1];
> text
> -------------------
> {{meeting,lunch}}
> (1 row)
>
> dynacom=# SELECT
> (CAST( '{{meeting,lunch},{training,presentation}}' as text[][]))[1:1][1];
> text
> -------------
> {{meeting}}
> (1 row)
>
> dynacom=# SELECT
> (CAST( '{{meeting,lunch},{training,presentation}}' as text[][]))[1:1][2];
> text
> -------------------
> {{meeting,lunch}}
> (1 row)
>
> dynacom=# SELECT
> (CAST( '{{meeting,lunch},{training,presentation}}' as text[][]))[1:1][3];
> text
> -------------------
> {{meeting,lunch}}
> (1 row)
>
> dynacom=# SELECT
> (CAST( '{{meeting,lunch},{training,presentation}}' as text[][]))[1:1][1000];
> text
> -------------------
> {{meeting,lunch}}
> (1 row)
>
> dynacom=#
>
> >
> > Achilleas Mantzios wrote:
> > > ???? ?????? 15 ??????????? 2007 18:55, ?/? chrisj ??????:
> > >> Thanks Achilleas,
> > >>
> > >> I see what you are saying, but if we consider just the index "[2]" for a
> > >> moment,
> > >> it means something different depending upon the context (in one case it
> > >> means "2" and in the other case it means "1:2") and the context is
> > >> determined by the format of indexes on other dimensions.
> > >>
> > >> I believe I understand....but incredibly confusing.
> > >
> > > Now that i think about it again, i speculate that the [2] is discarded.
> > >
> > >> - chris
> > >>
> > >> Achilleas Mantzios wrote:
> > >> > ???????? ?????????????? 14 ?????????????????????? 2007 21:31, ??/??
> > >>
> > >> chrisj
> > >
> > > ????????????:
> > >> >> given the following table:
> > >> >>
> > >> >> protocal2=> select * from sal_emp ;
> > >> >> name | pay_by_quarter | schedule
> > >>
> > >> -------+---------------------------+------------------------------------
> > >>
> > >> >>--- ---- Bill | {10000,10000,10000,10000} |
> > >> >> {{meeting,lunch},{training,presentation}}
> > >> >> Carol | {20000,25000,25000,25000} |
> > >> >> {{breakfast,consulting},{meeting,lunch}}
> > >> >> (2 rows)
> > >> >>
> > >> >> why do the following two queries yield different results??
> > >> >>
> > >> >> protocal2=> SELECT schedule[1][2] FROM sal_emp WHERE name = 'Bill';
> > >> >> schedule
> > >> >> ----------
> > >> >> lunch
> > >> >> (1 row)
> > >> >>
> > >> >> protocal2=> SELECT schedule[1:1][2] FROM sal_emp WHERE name = 'Bill';
> > >> >> schedule
> > >> >> -------------------
> > >> >> {{meeting,lunch}}
> > >> >> (1 row)
> > >> >
> > >> > The [n:m] notation denotes a slice of the array (not element).
> > >> > So schedule[1][2] is the Array element on 2nd col of 1st row,
> > >> > while schedule[1:1][2] could mean
> > >> > the second row of the subarray schedule[1:1][1:2].
> > >> > So these two are foundamentally different things.
> > >> > In my 7.4 even if you gave
> > >> > SELECT schedule[1:1][888] FROM sal_emp WHERE name = 'Bill';
> > >> > you would still get {{meeting,lunch}} as a result.
> > >> > (Right or wrong is another story).
> > >> > Anyway the first time you query for a "text",
> > >> > the second time you query for a "text[]", so you should expect
> > >> > different results.
> > >> > --
> > >> > Achilleas Mantzios
> > >> >
> > >> > ---------------------------(end of
> > >>
> > >> broadcast)---------------------------
> > >>
> > >> > TIP 3: Have you checked our extensive FAQ?
> > >> >
> > >> > http://www.postgresql.org/docs/faq
> > >
> > > --
> > > Achilleas Mantzios
> > >
> > > ---------------------------(end of broadcast)---------------------------
> > > TIP 3: Have you checked our extensive FAQ?
> > >
> > > http://www.postgresql.org/docs/faq
>
> --
> Achilleas Mantzios
>
> ---------------------------(end of broadcast)---------------------------
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--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://www.enterprisedb.com

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