Tom Lane wrote:
> Bruce Momjian <[EMAIL PROTECTED]> writes:
> > Tom Lane wrote:
> >> This is not a bug, this is a definitional disagreement, and your TODO
> >> entry presupposes an answer that I don't particularly agree with.
>
> > Well, our documentation suggests thaat [1] is the same as [1:1]:
> > http://www.postgresql.org/docs/8.2/static/arrays.html#AEN5791
>
> It says absolutely no such thing. A subscript expression involving m:n
> produces a "slice", hence an array of different dimensionality from the
> original, whereas a subscript expression not involving any colon
> produces a single element --- that is, not an array at all.
>
> You could make a fair case that the (ARRAY[[1,2],[3,4]])[1] example
> should throw an error instead of returning null. But to claim it is
> the same as a slice expression is a typing violation.
I finally figured out what you were saying by reading the source code
and finding this comment in parse_node.c:
/*
* A list containing only single subscripts refers to a single array
* element. If any of the items are double subscripts (lower:upper), then
* the subscript expression means an array slice operation. In this case,
* we supply a default lower bound of 1 for any items that contain only a
* single subscript. We have to prescan the indirection list to see if
* there are any double subscripts.
*/
I have updated the array documentation to be clearer about how slices
are handled, patch attached.
--
Bruce Momjian <[EMAIL PROTECTED]> http://momjian.us
EnterpriseDB http://www.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
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
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