Обсуждение: Extracting single coordinate from a box

I'm wondering if anyone knows how to extract a single co-ordinate from the data
type "box".

I know that I can access a single co-ordinate from a "point" using the array
notation: p[0] or p[1] where p is of type "point".
I can extract a single "point" from a "box" with b[0] or b[1] where b is of
type "box".
But when I try something like b[0][0] the passer ignores the second array
subscript parameter and returns only a "point".

Many thanks in advance,
Donald Fraser.

"Donald Fraser" <demolish@cwgsy.net> writes:
> But when I try something like b[0][0] the passer ignores the second array
> subscript parameter and returns only a "point".

Try this:

regression=# select f1, (f1[1])[0] from box_tbl;
         f1          | f1
---------------------+-----
 (2,2),(0,0)         |   0
 (3,3),(1,1)         |   1
 (2.5,3.5),(2.5,2.5) | 2.5
 (3,3),(3,3)         |   3
(4 rows)

You need the extra parentheses because the two subscript operations need
to work on fundamentally different datatypes --- if you write f1[1][0]
you are asking to subscript a 2-D array which this isn't.

[ experiments further ... ]  Drat, seems that syntax works in 7.4 but
not 7.3.  Dunno if that will help you.

            regards, tom lane

Thanks for the quick response.

----- Original Message -----
> "Donald Fraser" <demolish@cwgsy.net> writes:
> > But when I try something like b[0][0] the passer ignores the second array
> > subscript parameter and returns only a "point".


> You need the extra parentheses because the two subscript operations need
> to work on fundamentally different datatypes --- if you write f1[1][0]
> you are asking to subscript a 2-D array which this isn't.
>
> [ experiments further ... ]  Drat, seems that syntax works in 7.4 but
> not 7.3.  Dunno if that will help you.

I'm using 7.3.4 at the moment and I tried the scenario of using parentheses,
which didn't work.
I wrote a function in the end to extract it, but it would have been more
elegant without it :-(

Thanks again
Donald

I think you are forgetting that a box is an array of one dimension with
two points.
So, the first point is B[0] and the second is B[1].


Donald Fraser wrote:
>
> Thanks for the quick response.
>
> ----- Original Message -----
> > "Donald Fraser" <demolish@cwgsy.net> writes:
> > > But when I try something like b[0][0] the passer ignores the second array
> > > subscript parameter and returns only a "point".
>
> > You need the extra parentheses because the two subscript operations need
> > to work on fundamentally different datatypes --- if you write f1[1][0]
> > you are asking to subscript a 2-D array which this isn't.
> >
> > [ experiments further ... ]  Drat, seems that syntax works in 7.4 but
> > not 7.3.  Dunno if that will help you.
>
> I'm using 7.3.4 at the moment and I tried the scenario of using parentheses,
> which didn't work.
> I wrote a function in the end to extract it, but it would have been more
> elegant without it :-(
>
> Thanks again
> Donald
>
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