Re: RangeType internal use

Horiguchi-san,

On 06-02-2015 PM 04:34, Kyotaro HORIGUCHI wrote:
> Hi, from nearby:)
>

Thank you!

>> I wonder why I cannot find a way to get a range type for a given (sub-)
>> type. I would like to build a RangeType from Datum's of lower and upper
>> bounds. Much like how construct_array() builds an ArrayType from a Datum
>> array of elements given elements' type info.
>>
>> Is there some way I do not seem to know? If not, would it be worthwhile
>> to make something like construct_range() that returns a RangeType given
>> Datum's of lower and upper bounds and subtype info?
>
> make_range needs the range type itself.
>
> On SQL interfalce, you can get range type coresponds to a base
> type by looking up the pg_range catalog.
>
> SELECT rngtypid::regtype, rngsubtype::regtype
> FROM pg_range WHERE rngsubtype = 'int'::regtype;
>
> rngtypid | rngsubtype
> -----------+------------
> int4range | integer
>
> But there's only one syscache for this catalog which takes range
> type id. So the reverse resolution rngsubtype->rngtype seems not
> available. TypeCahce has only comparison function info as surely
> available element related to range types but this wouldn't
> help. I think scanning the entire cache is not allowable even if
> possible.
>
> Perhaps what is needed is adding RANGESUBTYPE syscache but I
> don't know whether it is allowable or not.
>
> Thoughts?

Actually, I'm wondering if there is one-to-one mapping from rangetype to
subtype (and vice versa?), then this should be OK. But if not (that is
designers of range types thought there is not necessarily such a
mapping), then perhaps we could add, say, rngtypeisdefault flag to pg_range.

Perhaps following is not too pretty:

+
+/*
+ * get_rangetype_for_type
+ *
+ * returns a TypeCacheEntry for a range type of a given (sub-) type.
+ */
+TypeCacheEntry *
+get_rangetype_for_type(Oid subtypid)
+{
+ Relation relation;
+ SysScanDesc scan;
+ HeapTuple rangeTuple;
+ Oid rngsubtype;
+ Oid rngtypid = InvalidOid;
+
+ relation = heap_open(RangeRelationId, AccessShareLock);
+
+ scan = systable_beginscan(relation, InvalidOid, false,
+ NULL, 0, NULL);
+
+ while ((rangeTuple = systable_getnext(scan)) != NULL)
+ {
+ rngsubtype = ((Form_pg_range) GETSTRUCT(rangeTuple))->rngsubtype;
+
+ if (rngsubtype == subtypid)
+ {
+ rngtypid = ((Form_pg_range) GETSTRUCT(rangeTuple))->rngtypid;
+ break;
+ }
+ }
+
+ systable_endscan(scan);
+ heap_close(relation, AccessShareLock);
+
+ return(rngtypid != InvalidOid
+ ? lookup_type_cache(rngtypid, TYPECACHE_RANGE_INFO): NULL);
+}

Thanks,
Amit