Folks,
Please find attached a patch for $Subject.
Motivation:
When people are doing keyset pagination, the simple cases redound to
adding a WHERE that looks like
(a, b, c) > (most_recent_a, most_recent_b, most_recent_c)
which corresponds to an ORDER BY clause that looks like
ORDER BY a, b, c
The fun starts when there are mixes of ASC and DESC in the ORDER BY
clause. Reverse collations make this simpler by inverting the meaning
of > (or similar), which makes the rowtypes still sortable in a new
dictionary order, so the pagination would look like:
(a, b, c) > (most_recent_a, most_recent_b COLLATE "C_backwards",
most_recent_c)
with an ORDER BY like:
ORDER BY a, b DESC, c
What say?
Best,
David.
--
David Fetter <david(at)fetter(dot)org> http://fetter.org/
Phone: +1 415 235 3778
Remember to vote!
Consider donating to Postgres: http://www.postgresql.org/about/donate
>From cd603421da0d8e4fc19401f24f46da8a26d88d3c Mon Sep 17 00:00:00 2001
From: David Fetter <[email protected]>
Date: Sat, 16 Nov 2019 09:29:14 -0800
Subject: [PATCH v1] Reverse collations
To: hackers
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="------------2.23.0"
This is a multi-part message in MIME format.
--------------2.23.0
Content-Type: text/plain; charset=UTF-8; format=fixed
Content-Transfer-Encoding: 8bit
Make it possible to define collations which reverse the usual meanings
of <, <=, >, and >= for their corresponding collations.
This in turn makes it easier to do keyset pagination on text with mixes
of ASC and DESC in the ORDER BY.
diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 55694c4368..3086936515 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -2106,6 +2106,13 @@ SCRAM-SHA-256$<replaceable><iteration count></replaceable>:<replaceable>&l
<entry>Is the collation deterministic?</entry>
</row>
+ <row>
+ <entry><structfield>collisreverse</structfield></entry>
+ <entry><type>bool</type></entry>
+ <entry></entry>
+ <entry>Is the collation reversed?</entry>
+ </row>
+
<row>
<entry><structfield>collencoding</structfield></entry>
<entry><type>int4</type></entry>
diff --git a/doc/src/sgml/ref/create_collation.sgml b/doc/src/sgml/ref/create_collation.sgml
index def4dda6e8..cb913871b7 100644
--- a/doc/src/sgml/ref/create_collation.sgml
+++ b/doc/src/sgml/ref/create_collation.sgml
@@ -24,7 +24,8 @@ CREATE COLLATION [ IF NOT EXISTS ] <replaceable>name</replaceable> (
[ LC_CTYPE = <replaceable>lc_ctype</replaceable>, ]
[ PROVIDER = <replaceable>provider</replaceable>, ]
[ DETERMINISTIC = <replaceable>boolean</replaceable>, ]
- [ VERSION = <replaceable>version</replaceable> ]
+ [ VERSION = <replaceable>version</replaceable>, ]
+ [ REVERSE = <replaceable>boolean</replaceable> ]
)
CREATE COLLATION [ IF NOT EXISTS ] <replaceable>name</replaceable> FROM <replaceable>existing_collation</replaceable>
</synopsis>
@@ -166,6 +167,16 @@ CREATE COLLATION [ IF NOT EXISTS ] <replaceable>name</replaceable> FROM <replace
</listitem>
</varlistentry>
+ <varlistentry>
+ <term><literal>REVERSE</literal></term>
+
+ <listitem>
+ <para>
+ Specifies whether the collation should sort in reverse. Defaults to false.
+ </para>
+ </listitem>
+ </varlistentry>
+
<varlistentry>
<term><replaceable>existing_collation</replaceable></term>
@@ -225,6 +236,13 @@ CREATE COLLATION german_phonebook (provider = icu, locale = 'de-u-co-phonebk');
</programlisting>
</para>
+ <para>
+ To create a collation from the <literal>C</literal> locale that sorts backwards:
+<programlisting>
+CREATE COLLATION C_sdrawckab (locale = 'C', reverse = true);
+</programlisting>
+ </para>
+
<para>
To create a collation from an existing collation:
<programlisting>
diff --git a/src/backend/catalog/pg_collation.c b/src/backend/catalog/pg_collation.c
index dd99d53547..6198f77f36 100644
--- a/src/backend/catalog/pg_collation.c
+++ b/src/backend/catalog/pg_collation.c
@@ -47,6 +47,7 @@ CollationCreate(const char *collname, Oid collnamespace,
Oid collowner,
char collprovider,
bool collisdeterministic,
+ bool collisreverse,
int32 collencoding,
const char *collcollate, const char *collctype,
const char *collversion,
@@ -162,6 +163,7 @@ CollationCreate(const char *collname, Oid collnamespace,
values[Anum_pg_collation_collowner - 1] = ObjectIdGetDatum(collowner);
values[Anum_pg_collation_collprovider - 1] = CharGetDatum(collprovider);
values[Anum_pg_collation_collisdeterministic - 1] = BoolGetDatum(collisdeterministic);
+ values[Anum_pg_collation_collisreverse - 1] = BoolGetDatum(collisreverse);
values[Anum_pg_collation_collencoding - 1] = Int32GetDatum(collencoding);
namestrcpy(&name_collate, collcollate);
values[Anum_pg_collation_collcollate - 1] = NameGetDatum(&name_collate);
diff --git a/src/backend/commands/collationcmds.c b/src/backend/commands/collationcmds.c
index 919e092483..ab37705b27 100644
--- a/src/backend/commands/collationcmds.c
+++ b/src/backend/commands/collationcmds.c
@@ -60,11 +60,13 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
DefElem *lcctypeEl = NULL;
DefElem *providerEl = NULL;
DefElem *deterministicEl = NULL;
+ DefElem *reverseEl = NULL;
DefElem *versionEl = NULL;
char *collcollate = NULL;
char *collctype = NULL;
char *collproviderstr = NULL;
bool collisdeterministic = true;
+ bool collisreverse = false;
int collencoding = 0;
char collprovider = 0;
char *collversion = NULL;
@@ -95,6 +97,8 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
defelp = &providerEl;
else if (strcmp(defel->defname, "deterministic") == 0)
defelp = &deterministicEl;
+ else if (strcmp(defel->defname, "reverse") == 0)
+ defelp = &reverseEl;
else if (strcmp(defel->defname, "version") == 0)
defelp = &versionEl;
else
@@ -130,6 +134,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
collctype = pstrdup(NameStr(((Form_pg_collation) GETSTRUCT(tp))->collctype));
collprovider = ((Form_pg_collation) GETSTRUCT(tp))->collprovider;
collisdeterministic = ((Form_pg_collation) GETSTRUCT(tp))->collisdeterministic;
+ collisreverse = ((Form_pg_collation) GETSTRUCT(tp))->collisreverse;
collencoding = ((Form_pg_collation) GETSTRUCT(tp))->collencoding;
ReleaseSysCache(tp);
@@ -165,6 +170,9 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
if (deterministicEl)
collisdeterministic = defGetBoolean(deterministicEl);
+ if (reverseEl)
+ collisreverse = defGetBoolean(reverseEl);
+
if (versionEl)
collversion = defGetString(versionEl);
@@ -222,6 +230,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
GetUserId(),
collprovider,
collisdeterministic,
+ collisreverse,
collencoding,
collcollate,
collctype,
@@ -605,7 +614,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
* about existing ones.
*/
collid = CollationCreate(localebuf, nspid, GetUserId(),
- COLLPROVIDER_LIBC, true, enc,
+ COLLPROVIDER_LIBC, true, false, enc,
localebuf, localebuf,
get_collation_actual_version(COLLPROVIDER_LIBC, localebuf),
true, true);
@@ -666,7 +675,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
int enc = aliases[i].enc;
collid = CollationCreate(alias, nspid, GetUserId(),
- COLLPROVIDER_LIBC, true, enc,
+ COLLPROVIDER_LIBC, true, false, enc,
locale, locale,
get_collation_actual_version(COLLPROVIDER_LIBC, locale),
true, true);
@@ -728,7 +737,7 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
collid = CollationCreate(psprintf("%s-x-icu", langtag),
nspid, GetUserId(),
- COLLPROVIDER_ICU, true, -1,
+ COLLPROVIDER_ICU, true, false, -1,
collcollate, collcollate,
get_collation_actual_version(COLLPROVIDER_ICU, collcollate),
true, true);
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index fcdbaae37b..f9e47c8bff 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1155,7 +1155,8 @@ lookup_collation_cache(Oid collation, bool set_flags)
collcollate = NameStr(collform->collcollate);
collctype = NameStr(collform->collctype);
- cache_entry->collate_is_c = ((strcmp(collcollate, "C") == 0) ||
+ cache_entry->collate_is_c = !collform->collisreverse &&
+ ((strcmp(collcollate, "C") == 0) ||
(strcmp(collcollate, "POSIX") == 0));
cache_entry->ctype_is_c = ((strcmp(collctype, "C") == 0) ||
(strcmp(collctype, "POSIX") == 0));
@@ -1357,6 +1358,7 @@ pg_newlocale_from_collation(Oid collid)
memset(&result, 0, sizeof(result));
result.provider = collform->collprovider;
result.deterministic = collform->collisdeterministic;
+ result.reverse = collform->collisreverse;
if (collform->collprovider == COLLPROVIDER_LIBC)
{
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index 69165eb311..02cbcbd23d 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -1603,6 +1603,9 @@ varstr_cmp(const char *arg1, int len1, const char *arg2, int len2, Oid collid)
if (a2p != a2buf)
pfree(a2p);
+ if (collid != DEFAULT_COLLATION_OID && mylocale->reverse)
+ INVERT_COMPARE_RESULT(result);
+
return result;
}
#endif /* WIN32 */
@@ -1681,6 +1684,9 @@ varstr_cmp(const char *arg1, int len1, const char *arg2, int len2, Oid collid)
(!mylocale || mylocale->deterministic))
result = strcmp(a1p, a2p);
+ if (collid != DEFAULT_COLLATION_OID && mylocale->reverse)
+ INVERT_COMPARE_RESULT(result);
+
if (a1p != a1buf)
pfree(a1p);
if (a2p != a2buf)
diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index 27602fa49c..61daf205d8 100644
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -954,6 +954,22 @@ get_collation_isdeterministic(Oid colloid)
return result;
}
+bool
+get_collation_isreverse(Oid colloid)
+{
+ HeapTuple tp;
+ Form_pg_collation colltup;
+ bool result;
+
+ tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(colloid));
+ if (!HeapTupleIsValid(tp))
+ elog(ERROR, "cache lookup failed for collation %u", colloid);
+ colltup = (Form_pg_collation) GETSTRUCT(tp);
+ result = colltup->collisreverse;
+ ReleaseSysCache(tp);
+ return result;
+}
+
/* ---------- CONSTRAINT CACHE ---------- */
/*
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index 88a261d9bd..33e357c300 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -1712,8 +1712,8 @@ setup_collation(FILE *cmdfd)
* in pg_collation.h. But add it before reading system collations, so
* that it wins if libc defines a locale named ucs_basic.
*/
- PG_CMD_PRINTF("INSERT INTO pg_collation (oid, collname, collnamespace, collowner, collprovider, collisdeterministic, collencoding, collcollate, collctype)"
- "VALUES (pg_nextoid('pg_catalog.pg_collation', 'oid', 'pg_catalog.pg_collation_oid_index'), 'ucs_basic', 'pg_catalog'::regnamespace, %u, '%c', true, %d, 'C', 'C');\n\n",
+ PG_CMD_PRINTF("INSERT INTO pg_collation (oid, collname, collnamespace, collowner, collprovider, collisdeterministic, collisreverse, collencoding, collcollate, collctype)"
+ "VALUES (pg_nextoid('pg_catalog.pg_collation', 'oid', 'pg_catalog.pg_collation_oid_index'), 'ucs_basic', 'pg_catalog'::regnamespace, %u, '%c', true, false, %d, 'C', 'C');\n\n",
BOOTSTRAP_SUPERUSERID, COLLPROVIDER_LIBC, PG_UTF8);
/* Now import all collations we can find in the operating system */
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index bf69adc2f4..32801744b9 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -13466,6 +13466,7 @@ dumpCollation(Archive *fout, CollInfo *collinfo)
PGresult *res;
int i_collprovider;
int i_collisdeterministic;
+ int i_collisreverse;
int i_collcollate;
int i_collctype;
const char *collprovider;
@@ -13501,6 +13502,13 @@ dumpCollation(Archive *fout, CollInfo *collinfo)
appendPQExpBufferStr(query,
"true AS collisdeterministic, ");
+ if (fout->remoteVersion >= 130000)
+ appendPQExpBufferStr(query,
+ "collisreverse, ");
+ else
+ appendPQExpBufferStr(query,
+ "false as collisreverse, ");
+
appendPQExpBuffer(query,
"collcollate, "
"collctype "
@@ -13512,6 +13520,7 @@ dumpCollation(Archive *fout, CollInfo *collinfo)
i_collprovider = PQfnumber(res, "collprovider");
i_collisdeterministic = PQfnumber(res, "collisdeterministic");
+ i_collisreverse = PQfnumber(res, "collisreverse");
i_collcollate = PQfnumber(res, "collcollate");
i_collctype = PQfnumber(res, "collctype");
@@ -13540,6 +13549,9 @@ dumpCollation(Archive *fout, CollInfo *collinfo)
if (strcmp(PQgetvalue(res, 0, i_collisdeterministic), "f") == 0)
appendPQExpBufferStr(q, ", deterministic = false");
+ if (strcmp(PQgetvalue(res, 0, i_collisreverse), "t") == 0)
+ appendPQExpBufferStr(q, ", reverse = true");
+
if (strcmp(collcollate, collctype) == 0)
{
appendPQExpBufferStr(q, ", locale = ");
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index b3b9313b36..d87aa96915 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -4525,6 +4525,17 @@ listCollations(const char *pattern, bool verbose, bool showSystem)
gettext_noop("yes"),
gettext_noop("Deterministic?"));
+ if (pset.sversion >= 130000)
+ appendPQExpBuffer(&buf,
+ ",\n CASE WHEN c.collisreverse THEN '%s' ELSE '%s' END AS \"%s\"",
+ gettext_noop("yes"), gettext_noop("no"),
+ gettext_noop("Reverse?"));
+ else
+ appendPQExpBuffer(&buf,
+ ",\n '%s' AS \"%s\"",
+ gettext_noop("no"),
+ gettext_noop("Reverse?"));
+
if (verbose)
appendPQExpBuffer(&buf,
",\n pg_catalog.obj_description(c.oid, 'pg_collation') AS \"%s\"",
diff --git a/src/include/catalog/pg_collation.h b/src/include/catalog/pg_collation.h
index d3366f361d..929d521d05 100644
--- a/src/include/catalog/pg_collation.h
+++ b/src/include/catalog/pg_collation.h
@@ -34,6 +34,7 @@ CATALOG(pg_collation,3456,CollationRelationId)
Oid collowner; /* owner of collation */
char collprovider; /* see constants below */
bool collisdeterministic BKI_DEFAULT(t);
+ bool collisreverse BKI_DEFAULT(f);
int32 collencoding; /* encoding for this collation; -1 = "all" */
NameData collcollate; /* LC_COLLATE setting */
NameData collctype; /* LC_CTYPE setting */
@@ -63,6 +64,7 @@ extern Oid CollationCreate(const char *collname, Oid collnamespace,
Oid collowner,
char collprovider,
bool collisdeterministic,
+ bool collisreverse,
int32 collencoding,
const char *collcollate, const char *collctype,
const char *collversion,
diff --git a/src/include/utils/lsyscache.h b/src/include/utils/lsyscache.h
index c8df5bff9f..90e1fbc33a 100644
--- a/src/include/utils/lsyscache.h
+++ b/src/include/utils/lsyscache.h
@@ -92,6 +92,7 @@ extern void get_atttypetypmodcoll(Oid relid, AttrNumber attnum,
Oid *typid, int32 *typmod, Oid *collid);
extern char *get_collation_name(Oid colloid);
extern bool get_collation_isdeterministic(Oid colloid);
+extern bool get_collation_isreverse(Oid colloid);
extern char *get_constraint_name(Oid conoid);
extern char *get_language_name(Oid langoid, bool missing_ok);
extern Oid get_opclass_family(Oid opclass);
diff --git a/src/include/utils/pg_locale.h b/src/include/utils/pg_locale.h
index b4b3aa5843..d571eab4c6 100644
--- a/src/include/utils/pg_locale.h
+++ b/src/include/utils/pg_locale.h
@@ -83,6 +83,7 @@ struct pg_locale_struct
{
char provider;
bool deterministic;
+ bool reverse;
union
{
#ifdef HAVE_LOCALE_T
diff --git a/src/test/regress/expected/collate.out b/src/test/regress/expected/collate.out
index 0dee7d783a..2e51dde931 100644
--- a/src/test/regress/expected/collate.out
+++ b/src/test/regress/expected/collate.out
@@ -11,6 +11,7 @@
*/
CREATE SCHEMA collate_tests;
SET search_path = collate_tests;
+CREATE COLLATION "C_sdrawckab" (locale = 'C', reverse = true);
CREATE TABLE collate_test1 (
a int,
b text COLLATE "C" NOT NULL
@@ -66,6 +67,14 @@ SELECT * FROM collate_test1 WHERE b COLLATE "C" >= 'abc' COLLATE "C";
3 | bbc
(2 rows)
+SELECT * FROM collate_test1 WHERE b COLLATE "C_sdrawckab" >= 'abc' COLLATE "C_sdrawckab";
+ a | b
+---+-----
+ 1 | abc
+ 2 | Abc
+ 4 | ABD
+(3 rows)
+
SELECT * FROM collate_test1 WHERE b COLLATE "C" >= 'bbc' COLLATE "POSIX"; -- fail
ERROR: collation mismatch between explicit collations "C" and "POSIX"
LINE 1: ...* FROM collate_test1 WHERE b COLLATE "C" >= 'bbc' COLLATE "P...
@@ -682,8 +691,9 @@ SELECT collation for ((SELECT b FROM collate_test1 LIMIT 1));
-- must get rid of them.
--
DROP SCHEMA collate_tests CASCADE;
-NOTICE: drop cascades to 17 other objects
-DETAIL: drop cascades to table collate_test1
+NOTICE: drop cascades to 18 other objects
+DETAIL: drop cascades to collation "C_sdrawckab"
+drop cascades to table collate_test1
drop cascades to table collate_test_like
drop cascades to table collate_test2
drop cascades to type testdomain_p
diff --git a/src/test/regress/sql/collate.sql b/src/test/regress/sql/collate.sql
index 89de26a227..1317ad4733 100644
--- a/src/test/regress/sql/collate.sql
+++ b/src/test/regress/sql/collate.sql
@@ -13,6 +13,8 @@
CREATE SCHEMA collate_tests;
SET search_path = collate_tests;
+CREATE COLLATION "C_sdrawckab" (locale = 'C', reverse = true);
+
CREATE TABLE collate_test1 (
a int,
b text COLLATE "C" NOT NULL
@@ -42,6 +44,7 @@ INSERT INTO collate_test2 SELECT * FROM collate_test1;
SELECT * FROM collate_test1 WHERE b COLLATE "C" >= 'abc';
SELECT * FROM collate_test1 WHERE b >= 'abc' COLLATE "C";
SELECT * FROM collate_test1 WHERE b COLLATE "C" >= 'abc' COLLATE "C";
+SELECT * FROM collate_test1 WHERE b COLLATE "C_sdrawckab" >= 'abc' COLLATE "C_sdrawckab";
SELECT * FROM collate_test1 WHERE b COLLATE "C" >= 'bbc' COLLATE "POSIX"; -- fail
CREATE DOMAIN testdomain_p AS text COLLATE "POSIX";
--------------2.23.0--
