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Add current substring regular expression syntax

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SQL:1999 had syntax

    SUBSTRING(text FROM pattern FOR escapechar)

but this was replaced in SQL:2003 by the more clear

    SUBSTRING(text SIMILAR pattern ESCAPE escapechar)

but this was never implemented in PostgreSQL.  This patch adds that
new syntax as an alternative in the parser, and updates documentation
and tests to indicate that this is the preferred alternative now.

Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>
Reviewed-by: Vik Fearing <vik@postgresfriends.org>
Reviewed-by: Fabien COELHO <coelho@cri.ensmp.fr>
Discussion: https://www.postgresql.org/message-id/flat/a15db31c-d0f8-8ce0-9039-578a31758adb%402ndquadrant.com
This commit is contained in:
Peter Eisentraut
2020-06-29 11:04:42 +02:00
parent aafefb4dcb
commit 78c887679d
8 changed files with 77 additions and 34 deletions
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20
doc/src/sgml/func.sgml
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@ -2669,15 +2669,21 @@ repeat('Pg', 4) <returnvalue>PgPgPgPg</returnvalue>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>substring</function> ( <parameter>string</parameter> <type>text</type> <literal>SIMILAR</literal> <parameter>pattern</parameter> <type>text</type> <literal>ESCAPE</literal> <parameter>escape</parameter> <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para role="func_signature">
<function>substring</function> ( <parameter>string</parameter> <type>text</type> <literal>FROM</literal> <parameter>pattern</parameter> <type>text</type> <literal>FOR</literal> <parameter>escape</parameter> <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Extracts substring matching <acronym>SQL</acronym> regular expression;
see <xref linkend="functions-similarto-regexp"/>.
see <xref linkend="functions-similarto-regexp"/>. The first form has
been specified since SQL:2003; the second form was only in SQL:1999
and should be considered obsolete.
</para>
<para>
<literal>substring('Thomas' from '%#"o_a#"_' for '#')</literal>
<literal>substring('Thomas' similar '%#"o_a#"_' escape '#')</literal>
<returnvalue>oma</returnvalue>
</para></entry>
</row>
@ -5160,7 +5166,11 @@ cast(-44 as bit(12)) <lineannotation>111111010100</lineannotation>
The <function>substring</function> function with three parameters
provides extraction of a substring that matches an SQL
regular expression pattern. The function can be written according
to SQL99 syntax:
to standard SQL syntax:
<synopsis>
substring(<replaceable>string</replaceable> similar <replaceable>pattern</replaceable> escape <replaceable>escape-character</replaceable>)
</synopsis>
or using the now obsolete SQL:1999 syntax:
<synopsis>
substring(<replaceable>string</replaceable> from <replaceable>pattern</replaceable> for <replaceable>escape-character</replaceable>)
</synopsis>
@ -5201,8 +5211,8 @@ substring(<replaceable>string</replaceable>, <replaceable>pattern</replaceable>,
<para>
Some examples, with <literal>#&quot;</literal> delimiting the return string:
<programlisting>
substring('foobar' from '%#"o_b#"%' for '#') <lineannotation>oob</lineannotation>
substring('foobar' from '#"o_b#"%' for '#') <lineannotation>NULL</lineannotation>
substring('foobar' similar '%#"o_b#"%' escape '#') <lineannotation>oob</lineannotation>
substring('foobar' similar '#"o_b#"%' escape '#') <lineannotation>NULL</lineannotation>
</programlisting>
</para>
</sect2>