Hi again,
thanks for the updated patch.
TAMMON is not implemented, because glibc doesn't provide an
alternative form for abbreviated month names.
It is a question if it is better to raise an error, return a non
alternative name or just ignore this flag. I have not strong
opinion about this. Inside DCH_to_char the prefix TM is ignored when
it is not used. So I did the same.
The Locale standard actually mentions abbreviated alternative month
names as
"ab_alt_mon" (see [1]). I tested this by setting your TAMMONTH strftime
call to '%Ob'.
If we set the locale to Russian and call the function for May this
actually returns
an abbreviated version of the month name:
Breakpoint 1, cache_locale_time () at pg_locale.c:772
772 if (strftime_l(bufptr, MAX_L10N_DATA, "%Ob", timeinfo,
locale) <= 0)
(gdb) n
774 bufptr += MAX_L10N_DATA;
(gdb) print bufptr
$4 = 0x7ffde4554630 "май"
Compared to the TMMON form of May in Russian this actually makes a
difference:
postgres=# set lc_time='ru_RU.UTF8';
SET
postgres=# select to_char('2026-05-01'::date, 'TMMON');
to_char
---------
МАЯ
(1 row)
postgres=# select to_char('2026-05-01'::date, 'TAMMONTH');
to_char
---------
МАЙ
(1 row)
Again, TAMMONTH uses %Ob here. So I would argue for implementing the
abbreviated
forms too.
Code Review
===========
I am not sure if this condition can be ever true:
+ if (IS_SUFFIX_TM(n->suffix) && IS_SUFFIX_TAM(n->suffix))
In case this is not possible the subsequent error message will
never be
thrown and the whole block is dead code.
However, if there is a reason for this check, it would be nice to
have a comment mention it.
Yes, I badly expected that prefixes could be mixed. I checked the
code, and this is not possible, so I removed this check
I think you missed one occurrence in the current patch:
[bernd@paco patches]$ cat
v2-0001-introduce-tam-modifier-for-date-timestamp-formatting.patch |
grep -B4 together
+
+ if (IS_SUFFIX_TM(n->suffix) && IS_SUFFIX_TAM(n->suffix))
+ ereturn(escontext,,
+ (errcode(ERRCODE_INVALID_DATETIME_FORMAT),
+ errmsg("TM and TAM prefixes cannot be used
together")));
One thing I am not entirely sure about is this line:
+ if (strftime_l(bufptr, MAX_L10N_DATA, "%OB", timeinfo, locale)
<= 0)
+ strftimefail = true;
As far as I checked %OB is not supported on Windows:
https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/strftime-wcsftime-strftime-l-wcsftime-l?view=msvc-170
I was, however, not able to confirm this on a Windows machine
right now.
I might be able to do so on the weekend.
However, the same problem exists with older glibc versions not
supporting
%OB. As far as I understand strftime_l this will lead to it
returning 0 and
therefore setting strftimefail to true always. Since this if
statement
is evaluated
unconditionally I expect this to also influence the behaviour of TM.
I am afraid about this case too, and I expect maybe some fallback mode
there. But because
I have not a Window machine or some machine with older glibc I decided
to don't touch it
for this moment.
glibc older than 2.28 doesn't support %OB. On the second hand the
result of %B is probably
equal to expected result %B.
Turns out I was wrong about this one. For one, although %OB is not
supported, Windows
actually does fall back to %B when used:
postgres=# set lc_time='cs-CZ.UTF8';
SET
postgres=# SELECT to_char('2026-08-01'::date, 'TMMONTH');
to_char
---------
SRPEN
(1 row)
postgres=# SELECT to_char('2026-08-01'::date, 'TAMMONTH');
to_char
---------
SRPEN
(1 row)
The documentation for wcsftime even mentions this behaviour (see [2]).
Furthermore, strftime_l only returns 0 when the result string does not
fit the buffer (or the result is in fact empty, see [3]). The return
value of
a function call with unrecognized format is not defined. glibc seems to
default to returning the format string itself:
PS C:\Users\bernd> docker run --rm -it debian:8 bash -c 'LC_TIME=C date
"+%B"'
August
PS C:\Users\bernd> docker run --rm -it debian:8 bash -c 'LC_TIME=C date
"+%OB"'
%OB
In my opinion this function call is very unlikely to ever return 0
because %OB is not
defined. So I don't see an issue with that code segment after all, as
this patch does
not interfere with TM and the current documentation of this patch
mentions the
platform dependency of this feature. However, one could argue for
checking whether
%OB/%Ob is literally returned and manually falling back to %B/%b to
cover all bases
and make behaviour more consistent.
Nitpicking & Conclusion
=======================
I feel like the documentation could explicitly mention the difference
between TMMONTH and TAMMONTH (i.e., mentioning genitive and
nominative
like the Locale docs you mentioned do). I also think it would be
beneficial to
mention that this linguistic detail is specific to certain languages.
please, if you can write this part of the doc. My English is not good
enough to write well about these linguistic details.
It is a problem primarily for slavic languages - like Czech or Russian
- but maybe it can be a wide problem.
I attached a revised version of your patch to this message explaining the
difference from a linguistic standpoint. I also fixed the second
listitem not
mentioning the suppression of trailing white space by TAM.
As English is also not my first language, I would be very glad if any
native
speaker reading this could have a look over it. Any feedback is
appreciated!
Thank you very much for this immediate review
You are most welcome 🙂
Best
Bernd
[1] https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/V1_chap07.html
[2] https://en.cppreference.com/cpp/chrono/c/wcsftime
[3] https://man7.org/linux/man-pages/man3/strftime.3.html
From 40ac8c6f05df816d10259fe7deaab2d7be91401f Mon Sep 17 00:00:00 2001
From: "[email protected]" <[email protected]>
Date: Wed, 12 Aug 2026 07:03:28 +0200
Subject: [PATCH v3] introduce 'tam' modifier for date/timestamp formatting
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
glibc returns localized month names in the genitive case, but it also
provides alternative month names in the nominative case. The TAM prefix
allows you to retrieve this alternative name.
example:
SELECT to_char(date '2026-08-01', 'TMMONTH');
┌─────────┐
│ to_char │
╞═════════╡
│ SRPNA │
└─────────┘
(1 row)
SELECT to_char(date '2026-08-01', 'TAMMONTH');
┌─────────┐
│ to_char │
╞═════════╡
│ SRPEN │
└─────────┘
(1 row)
---
doc/src/sgml/func/func-formatting.sgml | 31 +++++-
src/backend/utils/adt/formatting.c | 103 +++++++++++++++---
src/backend/utils/adt/pg_locale.c | 9 +-
src/include/utils/pg_locale.h | 1 +
.../regress/expected/collate.linux.utf8.out | 28 +++++
src/test/regress/sql/collate.linux.utf8.sql | 12 ++
6 files changed, 165 insertions(+), 19 deletions(-)
diff --git a/doc/src/sgml/func/func-formatting.sgml b/doc/src/sgml/func/func-formatting.sgml
index e4edaf4f42..2c356e7e8e 100644
--- a/doc/src/sgml/func/func-formatting.sgml
+++ b/doc/src/sgml/func/func-formatting.sgml
@@ -477,6 +477,12 @@
<xref linkend="guc-lc-time"/>)</entry>
<entry><literal>TMMonth</literal></entry>
</row>
+ <row>
+ <entry><literal>TAM</literal> prefix</entry>
+ <entry>translation alternative mode (use localized alternative month names based on
+ <xref linkend="guc-lc-time"/>; see usage notes)</entry>
+ <entry><literal>TAMMonth</literal></entry>
+ </row>
<row>
<entry><literal>SP</literal> suffix</entry>
<entry>spell mode (not implemented)</entry>
@@ -504,8 +510,29 @@
<listitem>
<para>
- <literal>TM</literal> suppresses trailing blanks whether or
- not <literal>FM</literal> is specified.
+ <literal>TM</literal> and <literal>TAM</literal> suppress trailing
+ blanks whether or not <literal>FM</literal> is specified.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ <literal>TM</literal> and <literal>TAM</literal> both produce
+ localized month names according to <xref linkend="guc-lc-time"/>,
+ but they can differ for certain languages that inflect month names
+ (e.g., Slavic languages). In such languages <literal>TM</literal>
+ produces the form used together with a day number, which is often the
+ genitive case, while <literal>TAM</literal> produces the standalone
+ (nominative) form. For example, with <literal>lc_time</literal> set to
+ a Czech locale, <literal>to_char('2026-08-01'::date, 'TMMONTH')</literal>
+ returns <literal>SRPNA</literal> (genitive), whereas
+ <literal>to_char('2026-08-01'::date, 'TAMMONTH')</literal> returns
+ <literal>SRPEN</literal> (nominative). For languages that do not draw
+ this distinction, and for the <literal>C</literal> locale, the two
+ modifiers produce the same result. This distinction relies on
+ alternative month names being available from the underlying operating
+ system's locale support, so <literal>TAM</literal> may not be effective
+ on all platforms.
</para>
</listitem>
diff --git a/src/backend/utils/adt/formatting.c b/src/backend/utils/adt/formatting.c
index effad4c37d..42f7935ac7 100644
--- a/src/backend/utils/adt/formatting.c
+++ b/src/backend/utils/adt/formatting.c
@@ -553,6 +553,7 @@ do { \
#define DCH_SUFFIX_th 0x04
#define DCH_SUFFIX_SP 0x08
#define DCH_SUFFIX_TM 0x10
+#define DCH_SUFFIX_TAM 0x20
/*
* Suffix tests
@@ -594,16 +595,25 @@ IS_SUFFIX_TM(uint8 _s)
return (_s & DCH_SUFFIX_TM);
}
+static inline bool
+IS_SUFFIX_TAM(uint8 _s)
+{
+ return (_s & DCH_SUFFIX_TAM);
+}
+
/*
* Suffixes definition for DATE-TIME TO/FROM CHAR
*/
#define TM_SUFFIX_LEN 2
+#define TAM_SUFFIX_LEN 3
static const KeySuffix DCH_suff[] = {
{"FM", 2, DCH_SUFFIX_FM, SUFFTYPE_PREFIX},
{"fm", 2, DCH_SUFFIX_FM, SUFFTYPE_PREFIX},
{"TM", TM_SUFFIX_LEN, DCH_SUFFIX_TM, SUFFTYPE_PREFIX},
+ {"TAM", TAM_SUFFIX_LEN, DCH_SUFFIX_TAM, SUFFTYPE_PREFIX},
{"tm", 2, DCH_SUFFIX_TM, SUFFTYPE_PREFIX},
+ {"tam", 3, DCH_SUFFIX_TAM, SUFFTYPE_PREFIX},
{"TH", 2, DCH_SUFFIX_TH, SUFFTYPE_POSTFIX},
{"th", 2, DCH_SUFFIX_th, SUFFTYPE_POSTFIX},
{"SP", 2, DCH_SUFFIX_SP, SUFFTYPE_POSTFIX},
@@ -2786,11 +2796,26 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out, Oid col
INVALID_FOR_INTERVAL;
if (!tm->tm_mon)
break;
- if (IS_SUFFIX_TM(n->suffix))
+ if (IS_SUFFIX_TM(n->suffix) || IS_SUFFIX_TAM(n->suffix))
{
- char *str = str_toupper_z(localized_full_months[tm->tm_mon - 1], collid);
+ char *str;
+ char **localized_months;
+ int suffix_len;
- if (strlen(str) <= (n->key->len + TM_SUFFIX_LEN) * DCH_MAX_ITEM_SIZ)
+ if (IS_SUFFIX_TM(n->suffix))
+ {
+ localized_months = localized_full_months;
+ suffix_len = TM_SUFFIX_LEN;
+ }
+ else
+ {
+ localized_months = localized_alt_full_months;
+ suffix_len = TAM_SUFFIX_LEN;
+ }
+
+ str = str_toupper_z(localized_months[tm->tm_mon - 1], collid);
+
+ if (strlen(str) <= (n->key->len + suffix_len) * DCH_MAX_ITEM_SIZ)
strcpy(s, str);
else
ereport(ERROR,
@@ -2806,11 +2831,26 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out, Oid col
INVALID_FOR_INTERVAL;
if (!tm->tm_mon)
break;
- if (IS_SUFFIX_TM(n->suffix))
+ if (IS_SUFFIX_TM(n->suffix) || IS_SUFFIX_TAM(n->suffix))
{
- char *str = str_initcap_z(localized_full_months[tm->tm_mon - 1], collid);
+ char *str;
+ char **localized_months;
+ int suffix_len;
- if (strlen(str) <= (n->key->len + TM_SUFFIX_LEN) * DCH_MAX_ITEM_SIZ)
+ if (IS_SUFFIX_TM(n->suffix))
+ {
+ localized_months = localized_full_months;
+ suffix_len = TM_SUFFIX_LEN;
+ }
+ else
+ {
+ localized_months = localized_alt_full_months;
+ suffix_len = TAM_SUFFIX_LEN;
+ }
+
+ str = str_initcap_z(localized_months[tm->tm_mon - 1], collid);
+
+ if (strlen(str) <= (n->key->len + suffix_len) * DCH_MAX_ITEM_SIZ)
strcpy(s, str);
else
ereport(ERROR,
@@ -2826,11 +2866,26 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out, Oid col
INVALID_FOR_INTERVAL;
if (!tm->tm_mon)
break;
- if (IS_SUFFIX_TM(n->suffix))
+ if (IS_SUFFIX_TM(n->suffix) || IS_SUFFIX_TAM(n->suffix))
{
- char *str = str_tolower_z(localized_full_months[tm->tm_mon - 1], collid);
+ char *str;
+ char **localized_months;
+ int suffix_len;
- if (strlen(str) <= (n->key->len + TM_SUFFIX_LEN) * DCH_MAX_ITEM_SIZ)
+ if (IS_SUFFIX_TM(n->suffix))
+ {
+ localized_months = localized_full_months;
+ suffix_len = TM_SUFFIX_LEN;
+ }
+ else
+ {
+ localized_months = localized_alt_full_months;
+ suffix_len = TAM_SUFFIX_LEN;
+ }
+
+ str = str_tolower_z(localized_months[tm->tm_mon - 1], collid);
+
+ if (strlen(str) <= (n->key->len + suffix_len) * DCH_MAX_ITEM_SIZ)
strcpy(s, str);
else
ereport(ERROR,
@@ -3565,13 +3620,29 @@ DCH_from_char(FormatNode *node, const char *in, TmFromChar *out,
case DCH_MONTH:
case DCH_Month:
case DCH_month:
- if (!from_char_seq_search(&value, &s, months_full,
- IS_SUFFIX_TM(n->suffix) ? localized_full_months : NULL,
- collid,
- n, escontext))
- return;
- if (!from_char_set_int(&out->mm, value + 1, n, escontext))
- return;
+ {
+ char **months;
+
+ if (IS_SUFFIX_TM(n->suffix) && IS_SUFFIX_TAM(n->suffix))
+ ereturn(escontext,,
+ (errcode(ERRCODE_INVALID_DATETIME_FORMAT),
+ errmsg("TM and TAM prefixes cannot be used together")));
+
+ if (IS_SUFFIX_TM(n->suffix))
+ months = localized_full_months;
+ else if (IS_SUFFIX_TAM(n->suffix))
+ months = localized_alt_full_months;
+ else
+ months = NULL;
+
+ if (!from_char_seq_search(&value, &s, months_full,
+ months,
+ collid,
+ n, escontext))
+ return;
+ if (!from_char_set_int(&out->mm, value + 1, n, escontext))
+ return;
+ }
break;
case DCH_MON:
case DCH_Mon:
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index 9eb99487e5..34d758486b 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -102,6 +102,7 @@ char *localized_abbrev_days[7 + 1];
char *localized_full_days[7 + 1];
char *localized_abbrev_months[12 + 1];
char *localized_full_months[12 + 1];
+char *localized_alt_full_months[12 + 1];
static pg_locale_t default_locale = NULL;
@@ -701,7 +702,7 @@ cache_single_string(char **dst, const char *src, int encoding)
void
cache_locale_time(void)
{
- char buf[(2 * 7 + 2 * 12) * MAX_L10N_DATA];
+ char buf[(2 * 7 + 3 * 12) * MAX_L10N_DATA];
char *bufptr;
time_t timenow;
struct tm *timeinfo;
@@ -768,6 +769,9 @@ cache_locale_time(void)
if (strftime_l(bufptr, MAX_L10N_DATA, "%B", timeinfo, locale) <= 0)
strftimefail = true;
bufptr += MAX_L10N_DATA;
+ if (strftime_l(bufptr, MAX_L10N_DATA, "%OB", timeinfo, locale) <= 0)
+ strftimefail = true;
+ bufptr += MAX_L10N_DATA;
}
#ifdef WIN32
@@ -824,9 +828,12 @@ cache_locale_time(void)
bufptr += MAX_L10N_DATA;
cache_single_string(&localized_full_months[i], bufptr, encoding);
bufptr += MAX_L10N_DATA;
+ cache_single_string(&localized_alt_full_months[i], bufptr, encoding);
+ bufptr += MAX_L10N_DATA;
}
localized_abbrev_months[12] = NULL;
localized_full_months[12] = NULL;
+ localized_alt_full_months[12] = NULL;
CurrentLCTimeValid = true;
}
diff --git a/src/include/utils/pg_locale.h b/src/include/utils/pg_locale.h
index b74821fdfa..3f79d4f0c1 100644
--- a/src/include/utils/pg_locale.h
+++ b/src/include/utils/pg_locale.h
@@ -43,6 +43,7 @@ extern PGDLLIMPORT char *localized_abbrev_days[];
extern PGDLLIMPORT char *localized_full_days[];
extern PGDLLIMPORT char *localized_abbrev_months[];
extern PGDLLIMPORT char *localized_full_months[];
+extern PGDLLIMPORT char *localized_alt_full_months[];
extern bool check_locale(int category, const char *locale, char **canonname);
extern char *pg_perm_setlocale(int category, const char *locale);
diff --git a/src/test/regress/expected/collate.linux.utf8.out b/src/test/regress/expected/collate.linux.utf8.out
index e0a39e4c30..26a03ac453 100644
--- a/src/test/regress/expected/collate.linux.utf8.out
+++ b/src/test/regress/expected/collate.linux.utf8.out
@@ -463,7 +463,22 @@ SELECT to_char(date '2010-04-01', 'DD TMMON YYYY' COLLATE "tr_TR");
01 NİS 2010
(1 row)
+-- to_char
+SET lc_time TO 'cs_CZ';
+SELECT to_char(date '2010-02-01', 'DD TMMONTH');
+ to_char
+----------
+ 01 ÚNORA
+(1 row)
+
+SELECT to_char(date '2010-02-01', 'TAMMONTH');
+ to_char
+---------
+ ÚNOR
+(1 row)
+
-- to_date
+SET lc_time TO 'tr_TR';
SELECT to_date('01 ŞUB 2010', 'DD TMMON YYYY');
to_date
------------
@@ -497,6 +512,19 @@ SELECT to_date('2010 01 araLık', 'YYYY DD TMMONTH');
12-01-2010
(1 row)
+SET lc_time TO 'cs_CZ';
+SELECT to_date('1 srpna 2010', 'DD TMMONTH YYYY');
+ to_date
+------------
+ 08-01-2010
+(1 row)
+
+SELECT to_date('1 srpen 2010', 'DD TAMMONTH YYYY');
+ to_date
+------------
+ 08-01-2010
+(1 row)
+
-- backwards parsing
CREATE VIEW collview1 AS SELECT * FROM collate_test1 WHERE b COLLATE "C" >= 'bbc';
CREATE VIEW collview2 AS SELECT a, b FROM collate_test1 ORDER BY b COLLATE "C";
diff --git a/src/test/regress/sql/collate.linux.utf8.sql b/src/test/regress/sql/collate.linux.utf8.sql
index 6d726ee9c9..3e7c356adb 100644
--- a/src/test/regress/sql/collate.linux.utf8.sql
+++ b/src/test/regress/sql/collate.linux.utf8.sql
@@ -182,7 +182,14 @@ SELECT to_char(date '2010-02-01', 'DD TMMON YYYY' COLLATE "tr_TR");
SELECT to_char(date '2010-04-01', 'DD TMMON YYYY');
SELECT to_char(date '2010-04-01', 'DD TMMON YYYY' COLLATE "tr_TR");
+-- to_char
+SET lc_time TO 'cs_CZ';
+
+SELECT to_char(date '2010-02-01', 'DD TMMONTH');
+SELECT to_char(date '2010-02-01', 'TAMMONTH');
+
-- to_date
+SET lc_time TO 'tr_TR';
SELECT to_date('01 ŞUB 2010', 'DD TMMON YYYY');
SELECT to_date('01 Şub 2010', 'DD TMMON YYYY');
@@ -192,6 +199,11 @@ SELECT to_date('01 Aralık 2010', 'DD TMMONTH YYYY');
SELECT to_date('01 aralık 2010', 'DD TMMONTH YYYY');
SELECT to_date('2010 01 araLık', 'YYYY DD TMMONTH');
+SET lc_time TO 'cs_CZ';
+
+SELECT to_date('1 srpna 2010', 'DD TMMONTH YYYY');
+SELECT to_date('1 srpen 2010', 'DD TAMMONTH YYYY');
+
-- backwards parsing
CREATE VIEW collview1 AS SELECT * FROM collate_test1 WHERE b COLLATE "C" >= 'bbc';
--
2.55.0
