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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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24
src/backend/utils/adt/pg_locale.c
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@@ -106,6 +106,8 @@ extern size_t strtitle_builtin(char *dst, size_t dstsize, const char *src,
ssize_t srclen, pg_locale_t locale);
extern size_t strupper_builtin(char *dst, size_t dstsize, const char *src,
ssize_t srclen, pg_locale_t locale);
extern size_t strfold_builtin(char *dst, size_t dstsize, const char *src,
ssize_t srclen, pg_locale_t locale);
extern size_t strlower_icu(char *dst, size_t dstsize, const char *src,
ssize_t srclen, pg_locale_t locale);
@@ -113,6 +115,8 @@ 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);
extern size_t strlower_libc(char *dst, size_t dstsize, const char *src,
ssize_t srclen, pg_locale_t locale);
@@ -1447,6 +1451,26 @@ pg_strupper(char *dst, size_t dstsize, const char *src, ssize_t srclen,
return 0; /* keep compiler quiet */
}
size_t
pg_strfold(char *dst, size_t dstsize, const char *src, ssize_t srclen,
pg_locale_t locale)
{
if (locale->provider == COLLPROVIDER_BUILTIN)
return strfold_builtin(dst, dstsize, src, srclen, locale);
#ifdef USE_ICU
else if (locale->provider == COLLPROVIDER_ICU)
return strfold_icu(dst, dstsize, src, srclen, locale);
#endif
/* for libc, just use strlower */
else if (locale->provider == COLLPROVIDER_LIBC)
return strlower_libc(dst, dstsize, src, srclen, locale);
else
/* shouldn't happen */
PGLOCALE_SUPPORT_ERROR(locale->provider);
return 0; /* keep compiler quiet */
}
/*
* pg_strcoll
*