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Add SQL function CASEFOLD().

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Useful for caseless matching. Similar to LOWER(), but avoids edge-case
problems with using LOWER() for caseless matching.

For collations that support it, CASEFOLD() handles characters with
more than two case variations or multi-character case variations. Some
characters may fold to uppercase. The results of case folding are also
more stable across Unicode versions than LOWER() or UPPER().

Discussion: https://postgr.es/m/a1886ddfcd8f60cb3e905c93009b646b4cfb74c5.camel%40j-davis.com
Reviewed-by: Ian Lawrence Barwick
This commit is contained in:
Jeff Davis
2025-01-24 14:56:22 -08:00
parent f15538cd27
commit bfc5992069
14 changed files with 278 additions and 3 deletions
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58
src/backend/utils/adt/pg_locale_icu.c
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@@ -54,6 +54,8 @@ extern size_t strtitle_icu(char *dst, size_t dstsize, const char *src,
ssize_t srclen, pg_locale_t locale);
extern size_t strupper_icu(char *dst, size_t dstsize, const char *src,
ssize_t srclen, pg_locale_t locale);
extern size_t strfold_icu(char *dst, size_t dstsize, const char *src,
ssize_t srclen, pg_locale_t locale);
#ifdef USE_ICU
@@ -117,6 +119,10 @@ static int32_t u_strToTitle_default_BI(UChar *dest, int32_t destCapacity,
const UChar *src, int32_t srcLength,
const char *locale,
UErrorCode *pErrorCode);
static int32_t u_strFoldCase_default(UChar *dest, int32_t destCapacity,
const UChar *src, int32_t srcLength,
const char *locale,
UErrorCode *pErrorCode);
static const struct collate_methods collate_methods_icu = {
.strncoll = strncoll_icu,
@@ -439,6 +445,26 @@ strupper_icu(char *dest, size_t destsize, const char *src, ssize_t srclen,
return result_len;
}
size_t
strfold_icu(char *dest, size_t destsize, const char *src, ssize_t srclen,
pg_locale_t locale)
{
int32_t len_uchar;
int32_t len_conv;
UChar *buff_uchar;
UChar *buff_conv;
size_t result_len;
len_uchar = icu_to_uchar(&buff_uchar, src, srclen);
len_conv = icu_convert_case(u_strFoldCase_default, locale,
&buff_conv, buff_uchar, len_uchar);
result_len = icu_from_uchar(dest, destsize, buff_conv, len_conv);
pfree(buff_uchar);
pfree(buff_conv);
return result_len;
}
/*
* strncoll_icu_utf8
*
@@ -673,6 +699,38 @@ u_strToTitle_default_BI(UChar *dest, int32_t destCapacity,
NULL, locale, pErrorCode);
}
static int32_t
u_strFoldCase_default(UChar *dest, int32_t destCapacity,
const UChar *src, int32_t srcLength,
const char *locale,
UErrorCode *pErrorCode)
{
uint32 options = U_FOLD_CASE_DEFAULT;
char lang[3];
UErrorCode status;
/*
* Unlike the ICU APIs for lowercasing, titlecasing, and uppercasing, case
* folding does not accept a locale. Instead it just supports a single
* option relevant to Turkic languages 'az' and 'tr'; check for those
* languages to enable the option.
*/
status = U_ZERO_ERROR;
uloc_getLanguage(locale, lang, 3, &status);
if (U_SUCCESS(status))
{
/*
* The option name is confusing, but it causes u_strFoldCase to use
* the 'T' mappings, which are ignored for U_FOLD_CASE_DEFAULT.
*/
if (strcmp(lang, "tr") == 0 || strcmp(lang, "az") == 0)
options = U_FOLD_CASE_EXCLUDE_SPECIAL_I;
}
return u_strFoldCase(dest, destCapacity, src, srcLength,
options, pErrorCode);
}
/*
* strncoll_icu
*