Thread: AW: [HACKERS] Re: Regress tests reveal *serious* psql bug

> SELECT arrtest.a[1:3],
>           arrtest.b[1:1][1:2][1:2],
>           arrtest.c[1:2], 
>           arrtest.d[1:1][1:2]
>    FROM arrtest;

Sorry for the stupid question, but can sombody enlighten me.
Why was the ":" used in the first place ? I would expect to use a ','
for an array slice. No ?

As in: select arrtest.a[1,1][1,2]
(This is also what others use for array slices)

Andreas

Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at> writes:
> Why was the ":" used in the first place ? I would expect to use a ','
> for an array slice. No ?

I'd think a comma is a separator between subscripts for different
dimensions, ie, a[1,2] would be equivalent to a[1][2].  It'd
certainly surprise *me* if it were interpreted as a slice indicator.

In any case, we're stuck with the notation now, I fear.
        regards, tom lane

Zeugswetter Andreas SB wrote:

> > SELECT arrtest.a[1:3],
> >           arrtest.b[1:1][1:2][1:2],
> >           arrtest.c[1:2],
> >           arrtest.d[1:1][1:2]
> >    FROM arrtest;
>
> Sorry for the stupid question, but can sombody enlighten me.
> Why was the ":" used in the first place ? I would expect to use a ','
> for an array slice. No ?
>
> As in: select arrtest.a[1,1][1,2]
> (This is also what others use for array slices)

In Fortran 90 (one of the few languages that has true arrays with a size
as well as a shape) arrays are indexed as
   A(1:8:2, -2:10)

which would mean the 2D array defined by rows (1,3,5,7) and columns
(-2,...,10). So ',' is commonly used to separate dimensions, and it
would be confusing to suddenly use commas to define a range. And as
Fortran is pretty much the grand-daddy of all programming languages we
can't really go and change that ;-) Putting indexes in separate ['s is
just a modern C'ism, because C has no real multi-dimensional arrays,
only pointer dereferencing.

Adriaan (a Fortran programmer)