Re: [BUGS] BUG #2913: Subscript on multidimensional array yields no value

Tom Lane wrote:
> Bruce Momjian <bruce@momjian.us> 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.

[ moved to docs list ]

Well, I don't understand our array documentation, so odds are others
don't either.  What are we saying here:

    An array slice is denoted by writing lower-bound:upper-bound for one or
    more array dimensions. For example, this query retrieves the first item
    on Bill's schedule for the first two days of the week:

    SELECT schedule[1:2][1:1] FROM sal_emp WHERE name = 'Bill';

            schedule
    ------------------------
     {{meeting},{training}}
    (1 row)

    We could also have written

    SELECT schedule[1:2][1] FROM sal_emp WHERE name = 'Bill';

    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 lower:upper. A lower bound of 1 is assumed for any subscript where
    only one value is specified, as in this example:

What is the difference between 'lower-bound:upper-bound' and
'lower:upper'?  Here are the items that confuse me:

    test=> SELECT (ARRAY[[1,2],[3,4]])[1][1];
     array
    -------
         1
    (1 row)

    test=> SELECT (ARRAY[[1,2],[3,4]])[1:1];
      array
    ---------
     {{1,2}}
    (1 row)

    test=> SELECT (ARRAY[[1,2],[3,4]])[1];
     array
    -------

    (1 row)

The first two make sense to me, but the last one does not.  If someone
explains it, I can update our documentation.

--
  Bruce Momjian   bruce@momjian.us
  EnterpriseDB    http://www.enterprisedb.com

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