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A little wordsmithing in the pattern-matching section.

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Tom Lane 2000-12-16 19:33:23 +00:00
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doc/src/sgml/func.sgml
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@ -1,4 +1,4 @@
<!-- $Header: /cvsroot/pgsql/doc/src/sgml/func.sgml,v 1.42 2000/12/16 18:33:13 tgl Exp $ -->
<!-- $Header: /cvsroot/pgsql/doc/src/sgml/func.sgml,v 1.43 2000/12/16 19:33:23 tgl Exp $ -->
<chapter id="functions">
<title>Functions and Operators</title>
@ -805,12 +805,12 @@
<para>
If <replaceable>pattern</replaceable> does not contain percent
signs or underscore then the pattern only represents the string
signs or underscore, then the pattern only represents the string
itself; in that case <function>LIKE</function> acts like the
equals operator. An underscore (<literal>_</literal>) in
<replaceable>pattern</replaceable> stands for (matches) any single
character, a percent sign (<literal>%</literal>) matches zero or
more characters.
character; a percent sign (<literal>%</literal>) matches any string
of zero or more characters.
</para>
<informalexample>
@ -827,33 +827,39 @@
<para>
<function>LIKE</function> pattern matches always cover the entire
string. On order to match a pattern anywhere within a string, the
string. To match a pattern anywhere within a string, the
pattern must therefore start and end with a percent sign.
</para>
<para>
In order to match a literal underscore or percent sign, the
respective character in <replaceable>pattern</replaceable> must be
preceded by the active escape character. The default escape
To match a literal underscore or percent sign without matching
other characters, the respective character in
<replaceable>pattern</replaceable> must be
preceded by the escape character. The default escape
character is the backslash but a different one may be selected by
using the <literal>ESCAPE</literal> clause. When using the
backslash as escape character in literal strings it must be
doubled, because the backslash already has a special meaning in
string literals.
using the <literal>ESCAPE</literal> clause. To match the escape
character itself, write two escape characters.
</para>
<para>
Note that the backslash already has a special meaning in string
literals, so to write a pattern constant that contains a backslash
you must write two backslashes in the query. You can avoid this by
selecting a different escape character with <literal>ESCAPE</literal>.
</para>
<para>
The keyword <token>ILIKE</token> can be used instead of
<token>LIKE</token> to make the match case insensitive according
to the active locale. This is a
to the active locale. This is not in the SQL standard but is a
<productname>Postgres</productname> extension.
</para>
<para>
The operator <literal>~~</literal> is equivalent to
<function>LIKE</function>, <literal>~~*</literal> corresponds to
<literal>ILIKE</literal>. Finally, there are also
<literal>!~~</literal> and <literal>!~~*</literal> operators to
<function>LIKE</function>, and <literal>~~*</literal> corresponds to
<function>ILIKE</function>. There are also
<literal>!~~</literal> and <literal>!~~*</literal> operators that
represent <function>NOT LIKE</function> and <function>NOT
ILIKE</function>. All of these are also
<productname>Postgres</productname>-specific.
@ -864,25 +870,6 @@
<sect2 id="functions-regexp">
<title>POSIX Regular Expressions</title>
<para>
POSIX regular expressions provide a more powerful means for
pattern matching than the <function>LIKE</function> function.
Many Unix tools such as <command>egrep</command>,
<command>sed</command>, or <command>awk</command> use a pattern
matching language that is similar to the one described here.
</para>
<para>
A regular expression is a character sequence that is an
abbreviated definition of a set of strings (a <firstterm>regular
set</firstterm>). A string is said to match a regular expression
if it is a member of the regular set described by the regular
expression. Unlike the <function>LIKE</function> operator, a
regular expression also matches anywhere within a string, unless
the regular expression is explicitly anchored to the beginning or
end of the string.
</para>
<table>
<title>Regular Expression Match Operators</title>
@ -920,6 +907,29 @@
</tgroup>
</table>
<para>
POSIX regular expressions provide a more powerful means for
pattern matching than the <function>LIKE</function> function.
Many Unix tools such as <command>egrep</command>,
<command>sed</command>, or <command>awk</command> use a pattern
matching language that is similar to the one described here.
</para>
<para>
A regular expression is a character sequence that is an
abbreviated definition of a set of strings (a <firstterm>regular
set</firstterm>). A string is said to match a regular expression
if it is a member of the regular set described by the regular
expression. As with <function>LIKE</function>, pattern characters
match string characters exactly unless they are special characters
in the regular expression language --- but regular expressions use
different special characters than <function>LIKE</function> does.
Unlike <function>LIKE</function> patterns, a
regular expression is allowed to match anywhere within a string, unless
the regular expression is explicitly anchored to the beginning or
end of the string.
</para>
<!-- derived from the re_format.7 man page -->
<para>
@ -927,8 +937,8 @@
1003.2, come in two forms: modern REs (roughly those of
<command>egrep</command>; 1003.2 calls these
<quote>extended</quote> REs) and obsolete REs (roughly those of
<command>ed</command>; 1003.2 <quote>basic</quote> REs). Obsolete
REs are not available in <productname>Postgres</productname>.
<command>ed</command>; 1003.2 <quote>basic</quote> REs).
<productname>Postgres</productname> implements the modern form.
</para>
<para>
@ -1004,6 +1014,13 @@
<literal>\</literal>.
</para>
<para>
Note that the backslash (<literal>\</literal>) already has a special
meaning in string
literals, so to write a pattern constant that contains a backslash
you must write two backslashes in the query.
</para>
<para>
A <firstterm>bracket expression</firstterm> is a list of
characters enclosed in <literal>[]</literal>. It normally matches