Re: general purpose array_sort - Mailing list pgsql-hackers

On Mon, Sep 30, 2024 at 1:01 PM Junwang Zhao <zhjwpku@gmail.com> wrote:
>
> > I would suggest accepting:
> > asc
> > desc
> > asc nulls first
> > asc nulls last *
> > desc nulls first *
> > desc nulls last
> >
> > As valid inputs for "dir" - and that the starred options are the defaults when null position is omitted.
> >
> > In short, mimic create index.
> >
> > David J.
> >
>
> PFA v3 with David's suggestion addressed.
>

I think just adding 2 bool arguments (asc/desc, nulls last/not nulls
last) would be easier.
but either way, (i don't have a huge opinion)
but document the second argument, imagine case
SELECT array_sort('{a,B}'::text[] , E'aSc NulLs  LaST \t\r\n');
would be tricky?


errmsg("multidimensional arrays sorting are not supported")));
write a sql test to trigger the error message that would be great.

you can add two or one example to collate.icu.utf8.sql to demo that it
actually works with COLLATE  collation_name
like:
SELECT array_sort('{a,B}'::text[] COLLATE case_insensitive);
SELECT array_sort('{a,B}'::text[] COLLATE "C");


#define WHITESPACE " \t\n\r"
you may also check function scanner_isspace


+ typentry = (TypeCacheEntry *) fcinfo->flinfo->fn_extra;
+ if (typentry == NULL || typentry->type_id != elmtyp)
+ {
+ typentry = lookup_type_cache(elmtyp, sort_asc ? TYPECACHE_LT_OPR :
TYPECACHE_GT_OPR);
+ fcinfo->flinfo->fn_extra = (void *) typentry;
+ }
you need to one-time check typentry->lt_opr or typentry->gt_opr exists?
see CreateStatistics.
            /* Disallow data types without a less-than operator */
            type = lookup_type_cache(attForm->atttypid, TYPECACHE_LT_OPR);
            if (type->lt_opr == InvalidOid)
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("column \"%s\" cannot be used in
statistics because its type %s has no default btree operator class",
                                attname, format_type_be(attForm->atttypid))));