diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/func.sgml | 46 |
1 files changed, 44 insertions, 2 deletions
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml index 5678e7621a5..d2b0b059e65 100644 --- a/doc/src/sgml/func.sgml +++ b/doc/src/sgml/func.sgml @@ -2596,7 +2596,7 @@ SELECT NOT(ROW(table.*) IS NOT NULL) FROM TABLE; -- detect at least one null in <row> <entry role="func_table_entry"><para role="func_signature"> - <indexterm> + <indexterm id="function-lower"> <primary>lower</primary> </indexterm> <function>lower</function> ( <type>text</type> ) @@ -2657,7 +2657,7 @@ SELECT NOT(ROW(table.*) IS NOT NULL) FROM TABLE; -- detect at least one null in <row> <entry role="func_table_entry"><para role="func_signature"> - <indexterm> + <indexterm id="function-normalize"> <primary>normalize</primary> </indexterm> <indexterm> @@ -3112,6 +3112,48 @@ SELECT NOT(ROW(table.*) IS NOT NULL) FROM TABLE; -- detect at least one null in <row> <entry role="func_table_entry"><para role="func_signature"> <indexterm> + <primary>casefold</primary> + </indexterm> + <function>casefold</function> ( <type>text</type> ) + <returnvalue>text</returnvalue> + </para> + <para> + Performs case folding of the input string according to the collation. + Case folding is similar to case conversion, but the purpose of case + folding is to facilitate case-insensitive comparison of strings, + whereas the purpose of case conversion is to convert to a particular + cased form. This function can only be used when the server encoding + is <literal>UTF8</literal>. + </para> + <para> + Ordinarily, case folding simply converts to lowercase, but there are a + few notable exceptions depending on the collation. For instance, the + character <literal>Σ</literal> (U+03A3) has two lowercase forms: + <literal>σ</literal> (U+03C3) and <literal>ς</literal> (U+03C2); case + folding in the <literal>PG_C_UTF8</literal> collation maps all three + forms to <literal>σ</literal>. Additionally, the result is not + necessarily lowercase; some characters may be folded to uppercase. + </para> + <para> + Case folding may change the length of the string. For instance, in + the <literal>PG_UNICODE_FAST</literal> collation, <literal>ß</literal> + (U+00DF) folds to <literal>ss</literal>. + </para> + <para> + <function>casefold</function> can be used for Unicode Default Caseless + Matching. It does not always preserve the normalized form of the + input string (see <xref linkend="function-normalize"/>). + </para> + <para> + The <literal>libc</literal> provider doesn't support case folding, so + <function>casefold</function> is identical to <xref + linkend="function-lower"/>. + </para></entry> + </row> + + <row> + <entry role="func_table_entry"><para role="func_signature"> + <indexterm> <primary>left</primary> </indexterm> <function>left</function> ( <parameter>string</parameter> <type>text</type>, |