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A little wordsmithing in the pattern-matching section.
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‎doc/src/sgml/func.sgml

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<!-- $Header: /cvsroot/pgsql/doc/src/sgml/func.sgml,v 1.42 2000/12/16 18:33:13 tgl Exp $ -->
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<!-- $Header: /cvsroot/pgsql/doc/src/sgml/func.sgml,v 1.43 2000/12/16 19:33:23 tgl Exp $ -->
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<chapter id="functions">
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<title>Functions and Operators</title>
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<para>
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If <replaceable>pattern</replaceable> does not contain percent
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signs or underscore then the pattern only represents the string
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signs or underscore, then the pattern only represents the string
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itself; in that case <function>LIKE</function> acts like the
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equals operator. An underscore (<literal>_</literal>) in
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<replaceable>pattern</replaceable> stands for (matches) any single
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character, a percent sign (<literal>%</literal>) matches zero or
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more characters.
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character; a percent sign (<literal>%</literal>) matches any string
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of zero or more characters.
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</para>
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<informalexample>
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<para>
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<function>LIKE</function> pattern matches always cover the entire
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string. On order to match a pattern anywhere within a string, the
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string. To match a pattern anywhere within a string, the
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pattern must therefore start and end with a percent sign.
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</para>
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<para>
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In order to match a literal underscore or percent sign, the
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respective character in <replaceable>pattern</replaceable> must be
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preceded by the active escape character. The default escape
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To match a literal underscore or percent sign without matching
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other characters, the respective character in
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<replaceable>pattern</replaceable> must be
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preceded by the escape character. The default escape
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character is the backslash but a different one may be selected by
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using the <literal>ESCAPE</literal> clause. When using the
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backslash as escape character in literal strings it must be
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doubled, because the backslash already has a special meaning in
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string literals.
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using the <literal>ESCAPE</literal> clause. To match the escape
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character itself, write two escape characters.
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</para>
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<para>
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Note that the backslash already has a special meaning in string
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literals, so to write a pattern constant that contains a backslash
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you must write two backslashes in the query. You can avoid this by
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selecting a different escape character with <literal>ESCAPE</literal>.
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</para>
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<para>
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The keyword <token>ILIKE</token> can be used instead of
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<token>LIKE</token> to make the match case insensitive according
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to the active locale. This is a
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to the active locale. This is not in the SQL standard but is a
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<productname>Postgres</productname> extension.
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</para>
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<para>
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The operator <literal>~~</literal> is equivalent to
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<function>LIKE</function>, <literal>~~*</literal> corresponds to
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<literal>ILIKE</literal>. Finally, there are also
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<literal>!~~</literal> and <literal>!~~*</literal> operators to
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<function>LIKE</function>, and <literal>~~*</literal> corresponds to
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<function>ILIKE</function>. There are also
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<literal>!~~</literal> and <literal>!~~*</literal> operators that
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represent <function>NOT LIKE</function> and <function>NOT
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ILIKE</function>. All of these are also
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<productname>Postgres</productname>-specific.
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<sect2 id="functions-regexp">
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<title>POSIX Regular Expressions</title>
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<para>
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POSIX regular expressions provide a more powerful means for
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pattern matching than the <function>LIKE</function> function.
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Many Unix tools such as <command>egrep</command>,
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<command>sed</command>, or <command>awk</command> use a pattern
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matching language that is similar to the one described here.
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</para>
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<para>
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A regular expression is a character sequence that is an
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abbreviated definition of a set of strings (a <firstterm>regular
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set</firstterm>). A string is said to match a regular expression
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if it is a member of the regular set described by the regular
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expression. Unlike the <function>LIKE</function> operator, a
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regular expression also matches anywhere within a string, unless
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the regular expression is explicitly anchored to the beginning or
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end of the string.
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</para>
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<table>
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<title>Regular Expression Match Operators</title>
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</tgroup>
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</table>
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<para>
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POSIX regular expressions provide a more powerful means for
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pattern matching than the <function>LIKE</function> function.
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Many Unix tools such as <command>egrep</command>,
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<command>sed</command>, or <command>awk</command> use a pattern
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matching language that is similar to the one described here.
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</para>
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<para>
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A regular expression is a character sequence that is an
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abbreviated definition of a set of strings (a <firstterm>regular
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set</firstterm>). A string is said to match a regular expression
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if it is a member of the regular set described by the regular
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expression. As with <function>LIKE</function>, pattern characters
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match string characters exactly unless they are special characters
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in the regular expression language --- but regular expressions use
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different special characters than <function>LIKE</function> does.
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Unlike <function>LIKE</function> patterns, a
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regular expression is allowed to match anywhere within a string, unless
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the regular expression is explicitly anchored to the beginning or
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end of the string.
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</para>
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<!-- derived from the re_format.7 man page -->
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<para>
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Regular expressions (<quote>RE</quote>s), as defined in POSIX
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1003.2, come in two forms: modern REs (roughly those of
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<command>egrep</command>; 1003.2 calls these
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<quote>extended</quote> REs) and obsolete REs (roughly those of
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<command>ed</command>; 1003.2 <quote>basic</quote> REs). Obsolete
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REs are not available in <productname>Postgres</productname>.
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<command>ed</command>; 1003.2 <quote>basic</quote> REs).
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<productname>Postgres</productname> implements the modern form.
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</para>
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<para>
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<literal>\</literal>.
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</para>
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<para>
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Note that the backslash (<literal>\</literal>) already has a special
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meaning in string
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literals, so to write a pattern constant that contains a backslash
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you must write two backslashes in the query.
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</para>
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<para>
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A <firstterm>bracket expression</firstterm> is a list of
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characters enclosed in <literal>[]</literal>. It normally matches

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