>>>>> "David" == David Fetter <da...@fetter.org> writes:
First, in testing the patch I found there were indeed some missing
cases: the sortsupport version of the comparator needs to be fixed too.
I attach a draft addition to your patch, you should probably look at
adding test cases that need this to work.
David> (a, b, c) < ($1, $2 COLLATE "C_backwards", $3)
David> ...
David> ORDER BY a, b DESC, c
That would have to be:
WHERE (a, b COLLATE "C_backwards", c) < ($1, $2, $3)
...
ORDER BY a, b COLLATE "C_backwards", c
Adding the below patch to yours, I can get this on the regression test
db (note that this is a -O0 asserts build, timings may be slow relative
to a production build):
create collation "C_rev" ( LOCALE = "C", REVERSE = true );
create index on tenk1 (hundred, (stringu1::text collate "C_rev"), string4);
explain analyze
select hundred, stringu1::text, string4
from tenk1
where (hundred, stringu1::text COLLATE "C_rev", string4)
> (10, 'WKAAAA', 'VVVVxx')
order by hundred, (stringu1::text collate "C_rev"), string4
limit 5;
QUERY
PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------------
Limit (cost=0.29..1.28 rows=5 width=132) (actual time=0.029..0.038 rows=5
loops=1)
-> Index Scan using tenk1_hundred_stringu1_string4_idx on tenk1
(cost=0.29..1768.49 rows=8900 width=132) (actual time=0.028..0.036 rows=5
loops=1)
Index Cond: (ROW(hundred, ((stringu1)::text)::text, string4) > ROW(10,
'WKAAAA'::text, 'VVVVxx'::name))
Planning Time: 0.225 ms
Execution Time: 0.072 ms
(5 rows)
and I checked the results, and they look correct now.
--
Andrew (irc:RhodiumToad)
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index 02cbcbd23d..61ab9720c5 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -84,6 +84,7 @@ typedef struct
int last_returned; /* Last comparison result (cache) */
bool cache_blob; /* Does buf2 contain strxfrm() blob, etc? */
bool collate_c;
+ bool reverse;
Oid typid; /* Actual datatype (text/bpchar/bytea/name) */
hyperLogLogState abbr_card; /* Abbreviated key cardinality state */
hyperLogLogState full_card; /* Full key cardinality state */
@@ -2090,6 +2091,7 @@ varstr_sortsupport(SortSupport ssup, Oid typid, Oid collid)
/* Initialize */
sss->last_returned = 0;
sss->locale = locale;
+ sss->reverse = (locale != 0) && locale->reverse;
/*
* To avoid somehow confusing a strxfrm() blob and an original string,
@@ -2401,6 +2403,9 @@ varstrfastcmp_locale(char *a1p, int len1, char *a2p, int len2, SortSupport ssup)
(!sss->locale || sss->locale->deterministic))
result = strcmp(sss->buf1, sss->buf2);
+ if (sss->reverse)
+ INVERT_COMPARE_RESULT(result);
+
/* Cache result, perhaps saving an expensive strcoll() call next time */
sss->cache_blob = false;
sss->last_returned = result;
@@ -2663,6 +2668,13 @@ done:
*/
res = DatumBigEndianToNative(res);
+ /*
+ * Account for reverse-ordering locales by flipping the bits. Note that
+ * Datum is an unsigned type (uintptr_t).
+ */
+ if (sss->reverse)
+ res ^= ~(Datum)0;
+
/* Don't leak memory here */
if (PointerGetDatum(authoritative) != original)
pfree(authoritative);
