From: Bruce Momjian <bruce@momjian.us>
To: Achilleas Mantzios <achill@matrix.gatewaynet.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: can someone explain confusing array indexing nomenclature
Date: Tue, 20 Feb 2007 09:26:01 -0500 (EST)
Message-ID: <200702201426.l1KEQ1O18498@momjian.us> (raw)
In-Reply-To: <200702200942.18500.achill@matrix.gatewaynet.com>
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)---------------------------
> TIP 7: You can help support the PostgreSQL project by donating at
>
> http://www.postgresql.org/about/donate
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://www.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
Attachments:/pgpatches/array (text/x-diff, 1.5K) download
Index: doc/src/sgml/array.sgml
===================================================================
RCS file: /cvsroot/pgsql/doc/src/sgml/array.sgml,v
retrieving revision 1.56
diff -c -c -r1.56 array.sgml
*** doc/src/sgml/array.sgml 1 Feb 2007 00:28:16 -0000 1.56
--- doc/src/sgml/array.sgml 20 Feb 2007 03:43:28 -0000
***************
*** 243,260 ****
(1 row)
</programlisting>
! We could also have written:
<programlisting>
- SELECT schedule[1:2][1] FROM sal_emp WHERE name = 'Bill';- </programlisting>- - with the same result. An array subscripting operation is always taken to- represent an array slice if any of the subscripts are written in the form- <literal><replaceable>lower</replaceable>:<replaceable>upper</replaceable></literal>.- A lower bound of 1 is assumed for any subscript where only one value- is specified, as in this example:- <programlisting>
SELECT schedule[1:2][2] FROM sal_emp WHERE name = 'Bill';
schedule
--- 243,256 ----
(1 row)
</programlisting>
! If any dimmension is written as a slice, i.e contains a colon, then all
! dimmensions are treated as slices. If a dimmension is missing, it is
! assumed to be <literal>[1:1]</>. If a dimmension has only a single
! number (no colon), that dimmension is treated as being from <literal>1</>
! to the number specified. For example, <literal>[2]</> is treated as
! <literal>[1:2], as in this example:
<programlisting>
SELECT schedule[1:2][2] FROM sal_emp WHERE name = 'Bill';
schedule
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-sql@postgresql.org
Cc: bruce@momjian.us, achill@matrix.gatewaynet.com
Subject: Re: can someone explain confusing array indexing nomenclature
In-Reply-To: <200702201426.l1KEQ1O18498@momjian.us>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox