On Tue, Apr 1, 2025 at 10:41 PM David G. Johnston
<david.g.johns...@gmail.com> wrote:
>
> On Tue, Apr 1, 2025 at 6:15 AM Marcos Pegoraro <mar...@f10.com.br> wrote:
>>
>> Em ter., 1 de abr. de 2025 às 02:00, David G. Johnston
>> <david.g.johns...@gmail.com> escreveu:
>>
>> Wouldn't it be good to add the use of parentheses using posix ? It's useful
>> and rarely documented
>> <literal>substring('Thomas', '...$')</literal>
>> + <literal>substring('Email: johnj...@mymail.com, Name: John' from
>> '@(.*), Name')</literal>
>>
>
> Agreed. A second example using () would be good here.
>
actually,
section (9.7.3.)
https://www.postgresql.org/docs/current/functions-matching.html#FUNCTIONS-POSIX-REGEXP
already have example, like:
substring('foobar' from 'o(.)b')
new patch attached, split substr, substring to make review more easier.
v6-0001: add function argument name to function substr
v6-0002: add function argument name to function substring
v6-0002 incorporated some of the changes in v5-0002-v3-delta.patch.
some of the changes in v5-0002-v3-delta.patch are not related to this thread,
so I didn't incorporate them, right now.
From 736ff000500d8d87499eaef0fb7331960173c4e8 Mon Sep 17 00:00:00 2001
From: jian he <jian.universal...@gmail.com>
Date: Mon, 21 Jul 2025 11:58:37 +0800
Subject: [PATCH v6 1/2] add function argument name to substr.
HEAD
\df substr
List of functions
Schema | Name | Result data type | Argument data types | Type
------------+--------+------------------+-------------------------+------
pg_catalog | substr | bytea | bytea, integer | func
pg_catalog | substr | bytea | bytea, integer, integer | func
pg_catalog | substr | text | text, integer | func
pg_catalog | substr | text | text, integer, integer | func
with patch
\df substr
List of functions
Schema | Name | Result data type | Argument data types | Type
------------+--------+------------------+-------------------------------------------+------
pg_catalog | substr | bytea | bytes bytea, start integer | func
pg_catalog | substr | bytea | bytes bytea, start integer, count integer | func
pg_catalog | substr | text | string text, start integer | func
pg_catalog | substr | text | string text, start integer, count integer | func
discussion: https://postgr.es/m/CACJufxHTBkymh06D4mGKNe1YfRNFN+gFBybmygWk=ptmqu0...@mail.gmail.com
---
src/include/catalog/pg_proc.dat | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 1fc19146f46..2f29f3757a5 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -3706,6 +3706,7 @@
prosrc => 'rtrim' },
{ oid => '877', descr => 'extract portion of string',
proname => 'substr', prorettype => 'text', proargtypes => 'text int4 int4',
+ proargnames => '{string, start, count}',
prosrc => 'text_substr' },
{ oid => '878', descr => 'map a set of characters appearing in string',
proname => 'translate', prorettype => 'text', proargtypes => 'text text text',
@@ -3724,6 +3725,7 @@
prosrc => 'rtrim1' },
{ oid => '883', descr => 'extract portion of string',
proname => 'substr', prorettype => 'text', proargtypes => 'text int4',
+ proargnames => '{string, start}',
prosrc => 'text_substr_no_len' },
{ oid => '884', descr => 'trim selected characters from both ends of string',
proname => 'btrim', prorettype => 'text', proargtypes => 'text text',
@@ -6286,9 +6288,11 @@
prosrc => 'bytea_substr_no_len' },
{ oid => '2085', descr => 'extract portion of string',
proname => 'substr', prorettype => 'bytea', proargtypes => 'bytea int4 int4',
+ proargnames => '{bytes, start, count}',
prosrc => 'bytea_substr' },
{ oid => '2086', descr => 'extract portion of string',
proname => 'substr', prorettype => 'bytea', proargtypes => 'bytea int4',
+ proargnames => '{bytes, start}',
prosrc => 'bytea_substr_no_len' },
{ oid => '2014', descr => 'position of substring',
proname => 'position', prorettype => 'int4', proargtypes => 'bytea bytea',
--
2.34.1
From 8f36831bed5e6182f4034fa4ae4bd16fe5272460 Mon Sep 17 00:00:00 2001
From: jian he <jian.universal...@gmail.com>
Date: Mon, 21 Jul 2025 14:20:34 +0800
Subject: [PATCH v6 2/2] add function argument name to function substring
HEAD
\df substr
List of functions
Schema | Name | Result data type | Argument data types | Type
------------+-----------+------------------+-------------------------+------
pg_catalog | substring | bit | bit, integer | func
pg_catalog | substring | bit | bit, integer, integer | func
pg_catalog | substring | bytea | bytea, integer | func
pg_catalog | substring | bytea | bytea, integer, integer | func
pg_catalog | substring | text | text, integer | func
pg_catalog | substring | text | text, integer, integer | func
pg_catalog | substring | text | text, text | func
pg_catalog | substring | text | text, text, text | func
with patch
\df substring
Schema | Name | Result data type | Argument data types | Type
------------+-----------+------------------+--------------------------------------------------+------
pg_catalog | substring | bit | bits bit, start integer, count integer | func
pg_catalog | substring | bytea | bytes bytea, start integer | func
pg_catalog | substring | bytea | bytes bytea, start integer, count integer | func
pg_catalog | substring | bit | string bit, start integer | func
pg_catalog | substring | text | string text, pattern text | func
pg_catalog | substring | text | string text, pattern text, escape_character text | func
pg_catalog | substring | text | string text, start integer | func
pg_catalog | substring | text | string text, start integer, count integer | func
(8 rows)
discussion: https://postgr.es/m/CACJufxHTBkymh06D4mGKNe1YfRNFN+gFBybmygWk=ptmqu0...@mail.gmail.com
---
doc/src/sgml/func.sgml | 110 +++++++++++++++++++++--
src/backend/catalog/system_functions.sql | 2 +-
src/include/catalog/pg_proc.dat | 8 ++
3 files changed, 113 insertions(+), 7 deletions(-)
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index f5a0e0954a1..a26dbf6fe0a 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -3806,6 +3806,56 @@ SELECT NOT(ROW(table.*) IS NOT NULL) FROM TABLE; -- detect at least one null in
</para></entry>
</row>
+ <row>
+ <entry role="func_table_entry"><para role="func_signature">
+ <function>substring</function> ( <parameter>string</parameter> <type>text</type>, <parameter>pattern</parameter> <type>text</type> )
+ <returnvalue>text</returnvalue>
+ </para>
+ <para>
+ Extracts the first substring matching POSIX regular expression; see
+ <xref linkend="functions-posix-regexp"/>.
+ </para>
+ <para>
+ <literal>substring('Thomas', '...$')</literal>
+ <returnvalue>mas</returnvalue>
+ </para></entry>
+ </row>
+
+ <row>
+ <entry role="func_table_entry"><para role="func_signature">
+ <function>substring</function> ( <parameter>string</parameter> <type>text</type>, <parameter>pattern</parameter> <type>text</type>, <parameter>escape</parameter> <type>text</type>)
+ <returnvalue>text</returnvalue>
+ </para>
+ <para>
+ Extracts the first substring matching <acronym>SQL</acronym> regular expression;
+ see <xref linkend="functions-similarto-regexp"/>.
+ </para>
+ <para>
+ <literal>substring('Thomas', '%#"o_a#"_', '#')</literal>
+ <returnvalue>oma</returnvalue>
+ </para></entry>
+ </row>
+
+ <row>
+ <entry role="func_table_entry"><para role="func_signature">
+ <indexterm>
+ <primary>substring</primary>
+ </indexterm>
+ <function>substring</function> ( <parameter>string</parameter> <type>text</type>, <parameter>start</parameter> <type>integer</type> <optional>, <parameter>count</parameter> <type>integer</type> </optional> )
+ <returnvalue>text</returnvalue>
+ </para>
+ <para>
+ Extracts the substring of <parameter>string</parameter> starting at
+ the <parameter>start</parameter>'th character,
+ and stopping after <parameter>count</parameter> characters if that is
+ specified.
+ </para>
+ <para>
+ <literal>substring('Thomas', 2, 3)</literal>
+ <returnvalue>hom</returnvalue>
+ </para></entry>
+ </row>
+
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
@@ -4859,6 +4909,27 @@ SELECT format('Testing %3$s, %2$s, %s', 'one', 'two', 'three');
<returnvalue>\x5678</returnvalue>
</para></entry>
</row>
+
+ <row>
+ <entry role="func_table_entry"><para role="func_signature">
+ <indexterm>
+ <primary>substring</primary>
+ </indexterm>
+ <function>substring</function> ( <parameter>bytes</parameter> <type>bytea</type>, <parameter>start</parameter> <type>integer</type> <optional>, <parameter>count</parameter> <type>integer</type> </optional> )
+ <returnvalue>bytea</returnvalue>
+ </para>
+ <para>
+ Extracts the substring of <parameter>bytes</parameter> starting at
+ the <parameter>start</parameter>'th byte,
+ and stopping after <parameter>count</parameter> bytes if that is
+ specified.
+ </para>
+ <para>
+ <literal>substring('\x1234567890'::bytea, 3, 2)</literal>
+ <returnvalue>\x5678</returnvalue>
+ </para></entry>
+ </row>
+
</tbody>
</tgroup>
</table>
@@ -5401,6 +5472,26 @@ cast(-1234 as bytea) <lineannotation>\xfffffb2e</lineannotation>
</para></entry>
</row>
+ <row>
+ <entry role="func_table_entry"><para role="func_signature">
+ <indexterm>
+ <primary>substring</primary>
+ </indexterm>
+ <function>substring</function> ( <parameter>bits</parameter> <type>bit</type>, <parameter>start</parameter> <type>integer</type> <optional>, <parameter>count</parameter> <type>integer</type> </optional> )
+ <returnvalue>bit</returnvalue>
+ </para>
+ <para>
+ Extracts the substring of <parameter>bits</parameter> starting at
+ the <parameter>start</parameter>'th bit,
+ and stopping after <parameter>count</parameter> bits if that is
+ specified.
+ </para>
+ <para>
+ <literal>substring(B'110010111111', 3, 2)</literal>
+ <returnvalue>00</returnvalue>
+ </para></entry>
+ </row>
+
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
@@ -5413,6 +5504,7 @@ cast(-1234 as bytea) <lineannotation>\xfffffb2e</lineannotation>
Extracts the substring of <parameter>bits</parameter> starting at
the <parameter>start</parameter>'th bit if that is specified,
and stopping after <parameter>count</parameter> bits if that is
+ and stopping after <parameter>count</parameter> bits if that is
specified. Provide at least one of <parameter>start</parameter>
and <parameter>count</parameter>.
</para>
@@ -5864,7 +5956,7 @@ substring(<replaceable>string</replaceable> from <replaceable>pattern</replaceab
</synopsis>
or as a plain three-argument function:
<synopsis>
-substring(<replaceable>string</replaceable>, <replaceable>pattern</replaceable>, <replaceable>escape-character</replaceable>)
+substring(<replaceable>string</replaceable>, <replaceable>pattern</replaceable>, <replaceable>escape</replaceable>)
</synopsis>
As with <literal>SIMILAR TO</literal>, the
specified pattern must match the entire data string, or else the
@@ -6068,11 +6160,17 @@ substring('foobar' similar '#"o_b#"%' escape '#') <lineannotation>NULL</linea
</para>
<para>
- The <function>substring</function> function with two parameters,
- <function>substring(<replaceable>string</replaceable> from
- <replaceable>pattern</replaceable>)</function>, provides extraction of a
- substring
- that matches a POSIX regular expression pattern. It returns null if
+ The <function>substring</function> function with two parameters provides extraction of a
+ substring that matches a <acronym>POSIX</acronym> regular expression pattern.
+ The function can be written according to standard <acronym>SQL</acronym> syntax:
+<synopsis>
+substring(<replaceable>string</replaceable> FROM <replaceable>pattern</replaceable>)
+</synopsis>
+ It can also written as a plain two-argument function:
+<synopsis>
+substring(<replaceable>string</replaceable>, <replaceable>pattern</replaceable>)
+</synopsis>
+ It returns null if
there is no match, otherwise the first portion of the text that matched the
pattern. But if the pattern contains any parentheses, the portion
of the text that matched the first parenthesized subexpression (the
diff --git a/src/backend/catalog/system_functions.sql b/src/backend/catalog/system_functions.sql
index 566f308e443..544b549ae74 100644
--- a/src/backend/catalog/system_functions.sql
+++ b/src/backend/catalog/system_functions.sql
@@ -42,7 +42,7 @@ CREATE OR REPLACE FUNCTION rpad(text, integer)
IMMUTABLE PARALLEL SAFE STRICT COST 1
RETURN rpad($1, $2, ' ');
-CREATE OR REPLACE FUNCTION "substring"(text, text, text)
+CREATE OR REPLACE FUNCTION "substring"(string text, pattern text, escape text)
RETURNS text
LANGUAGE sql
IMMUTABLE PARALLEL SAFE STRICT COST 1
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 2f29f3757a5..6b8a918cdd6 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -3736,9 +3736,11 @@
{ oid => '936', descr => 'extract portion of string',
proname => 'substring', prorettype => 'text', proargtypes => 'text int4 int4',
+ proargnames => '{string, start, count}',
prosrc => 'text_substr' },
{ oid => '937', descr => 'extract portion of string',
proname => 'substring', prorettype => 'text', proargtypes => 'text int4',
+ proargnames => '{string, start}',
prosrc => 'text_substr_no_len' },
{ oid => '2087',
descr => 'replace all occurrences in string of old_substr with new_substr',
@@ -4156,6 +4158,7 @@
prosrc => 'bitcat' },
{ oid => '1680', descr => 'extract portion of bitstring',
proname => 'substring', prorettype => 'bit', proargtypes => 'bit int4 int4',
+ proargnames => '{bits, start, count}',
prosrc => 'bitsubstr' },
{ oid => '1681', descr => 'bitstring length',
proname => 'length', prorettype => 'int4', proargtypes => 'bit',
@@ -4185,6 +4188,7 @@
prosrc => 'bitposition' },
{ oid => '1699', descr => 'extract portion of bitstring',
proname => 'substring', prorettype => 'bit', proargtypes => 'bit int4',
+ proargnames => '{string, start}',
prosrc => 'bitsubstr_no_len' },
{ oid => '3030', descr => 'substitute portion of bitstring',
@@ -6282,9 +6286,11 @@
prosrc => 'byteacat' },
{ oid => '2012', descr => 'extract portion of string',
proname => 'substring', prorettype => 'bytea',
+ proargnames => '{bytes, start, count}',
proargtypes => 'bytea int4 int4', prosrc => 'bytea_substr' },
{ oid => '2013', descr => 'extract portion of string',
proname => 'substring', prorettype => 'bytea', proargtypes => 'bytea int4',
+ proargnames => '{bytes, start}',
prosrc => 'bytea_substr_no_len' },
{ oid => '2085', descr => 'extract portion of string',
proname => 'substr', prorettype => 'bytea', proargtypes => 'bytea int4 int4',
@@ -6484,9 +6490,11 @@
{ oid => '2073', descr => 'extract text matching regular expression',
proname => 'substring', prorettype => 'text', proargtypes => 'text text',
+ proargnames => '{string, pattern}',
prosrc => 'textregexsubstr' },
{ oid => '2074', descr => 'extract text matching SQL regular expression',
proname => 'substring', prolang => 'sql', prorettype => 'text',
+ proargnames => '{string, pattern, escape}',
proargtypes => 'text text text', prosrc => 'see system_functions.sql' },
{ oid => '2075', descr => 'convert int8 to bitstring',
--
2.34.1
