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]:
> >
> 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]>

  + 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)
!   We could also have written:
- 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';
--- 243,256 ----
  (1 row)
!   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:
  SELECT schedule[1:2][2] FROM sal_emp WHERE name = 'Bill';
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