P

Clément Lassieur <clement@lassieur.org> ezt írta (időpont: 2018. júl. 29.,
V 14:01):

> Danny Milosavljevic <dannym@scratchpost.org> writes:
>
> > Hi Tatiana,
> >
> > On Sun, 8 Jul 2018 21:48:32 +0200
> > Tatiana Sholokhova <tanja201396@gmail.com> wrote:
> >
> >> Do you have ideas on how to
> >> implement tuple comparison and other routines in SQL and guile in a
> >> convenient and flexible way?
> >
> > sqlite3 supports row values, so the comparison can be
> > written like this:
> >
> >   select * from foo where (a,b,c) = (2,'foo',3);
> >
> > It even supports NULLs for wildcards, though it's a little more
> complicated:
> >
> >   select * from foo where coalesce((a,b,c) = (2,NULL,3), 1) = 1;
> >
> > The sqlite C interface doesn't support parameter bindings for the entire
> > row, though, so you'd have to specify 3 values.
> >
> > This works:
> >
> >   (sqlite-exec db "select * from foo where (a,b,c) = (" 2 "," "foo" ","
> 3 ");")
> >
> > but this doesn't work, unfortunately:
> >
> >   (sqlite-exec db "select * from foo where (a,b,c) = " '(2 "foo" 3) ";")
> >
> > See also https://www.sqlite.org/rowvalue.html
>
> With the '<' operator, it doesn't give the results we are looking for, I
> think.
>
> For example:
>
> select (0,1) < (1,0); -- returns 1
> select (0,0) < (0,1); -- returns 1
>

This is working as expected. Actually this:
(a,b)<(c,d) is a shortcut for a<c or (a=c and b<d).

In both cases, we'd want it to return 0.
>

How do we use it? Why this is the expected result?


> I think we should use:
>
> select (0 < 1) and (1 < 0); -- returns 0
> select (0 < 0) and (0 < 1); -- returns 0
>

Could you please clarify which numbers are the placeholders for which
quantities?

>
> instead, for the pagination borders code.
>