0002-Add-current-substring-regular-expression-syntax.patch

From 32b6d132232d40308c47faad111e75d5c03f6b63 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Fri, 19 Jun 2020 11:14:10 +0200
Subject: [PATCH 2/2] Add current substring regular expression syntax

SQL99 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.
---
 doc/src/sgml/func.sgml                | 20 ++++++++++++-----
 src/backend/parser/gram.y             | 26 +++++++++++++++++++++-
 src/test/regress/expected/strings.out | 31 ++++++++++++++++-----------
 src/test/regress/sql/strings.sql      | 26 +++++++++++-----------
 4 files changed, 73 insertions(+), 30 deletions(-)

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 9d71678029..eedf189546 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -2669,15 +2669,21 @@ <title><acronym>SQL</acronym> String Functions and Operators</title>
 
       <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
+        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 @@ <title><function>SIMILAR TO</function> Regular Expressions</title>
     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 SQL99 syntax:
 <synopsis>
 substring(<replaceable>string</replaceable> from <replaceable>pattern</replaceable> for <replaceable>escape-character</replaceable>)
 </synopsis>
@@ -5201,8 +5211,8 @@ <title><function>SIMILAR TO</function> Regular Expressions</title>
    <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>
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 1a843049f0..5f21039b11 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -14451,7 +14451,27 @@ position_list:
 			| /*EMPTY*/								{ $$ = NIL; }
 		;
 
-/* SUBSTRING() arguments */
+/*
+ * SUBSTRING() arguments
+ *
+ * Note that SQL99 has both
+ *
+ * text FROM int FOR int
+ *
+ * and
+ *
+ * text FROM pattern FOR escape
+ *
+ * In the parser we map them both to a call to the substring() function and
+ * rely on type resolution to pick the right one.
+ *
+ * In SQL:2003, the second variant was changed to
+ *
+ * text SIMILAR pattern ESCAPE escape
+ *
+ * We could in theory map that to a different function internally, but
+ * since we still support the SQL99 version, we don't.
+ */
 substr_list:
 			a_expr FROM a_expr FOR a_expr
 				{
@@ -14483,6 +14503,10 @@ substr_list:
 									makeTypeCast($3,
 												 SystemTypeName("int4"), -1));
 				}
+			| a_expr SIMILAR a_expr ESCAPE a_expr
+				{
+					$$ = list_make3($1, $3, $5);
+				}
 			/*
 			 * We also want to support generic substring functions that
 			 * accept the usual generic list of arguments.
diff --git a/src/test/regress/expected/strings.out b/src/test/regress/expected/strings.out
index 6e98d183f6..8c034c9599 100644
--- a/src/test/regress/expected/strings.out
+++ b/src/test/regress/expected/strings.out
@@ -397,6 +397,13 @@ SELECT SUBSTRING('1234567890' FROM 4 FOR 3) = '456' AS "456";
 (1 row)
 
 -- T581 regular expression substring (with SQL's bizarre regexp syntax)
+SELECT SUBSTRING('abcdefg' SIMILAR 'a#"(b_d)#"%' ESCAPE '#') AS "bcd";
+ bcd 
+-----
+ bcd
+(1 row)
+
+-- obsolete SQL99 syntax
 SELECT SUBSTRING('abcdefg' FROM 'a#"(b_d)#"%' FOR '#') AS "bcd";
  bcd 
 -----
@@ -404,75 +411,75 @@ SELECT SUBSTRING('abcdefg' FROM 'a#"(b_d)#"%' FOR '#') AS "bcd";
 (1 row)
 
 -- No match should return NULL
-SELECT SUBSTRING('abcdefg' FROM '#"(b_d)#"%' FOR '#') IS NULL AS "True";
+SELECT SUBSTRING('abcdefg' SIMILAR '#"(b_d)#"%' ESCAPE '#') IS NULL AS "True";
  True 
 ------
  t
 (1 row)
 
 -- Null inputs should return NULL
-SELECT SUBSTRING('abcdefg' FROM '%' FOR NULL) IS NULL AS "True";
+SELECT SUBSTRING('abcdefg' SIMILAR '%' ESCAPE NULL) IS NULL AS "True";
  True 
 ------
  t
 (1 row)
 
-SELECT SUBSTRING(NULL FROM '%' FOR '#') IS NULL AS "True";
+SELECT SUBSTRING(NULL SIMILAR '%' ESCAPE '#') IS NULL AS "True";
  True 
 ------
  t
 (1 row)
 
-SELECT SUBSTRING('abcdefg' FROM NULL FOR '#') IS NULL AS "True";
+SELECT SUBSTRING('abcdefg' SIMILAR NULL ESCAPE '#') IS NULL AS "True";
  True 
 ------
  t
 (1 row)
 
 -- The first and last parts should act non-greedy
-SELECT SUBSTRING('abcdefg' FROM 'a#"%#"g' FOR '#') AS "bcdef";
+SELECT SUBSTRING('abcdefg' SIMILAR 'a#"%#"g' ESCAPE '#') AS "bcdef";
  bcdef 
 -------
  bcdef
 (1 row)
 
-SELECT SUBSTRING('abcdefg' FROM 'a*#"%#"g*' FOR '#') AS "abcdefg";
+SELECT SUBSTRING('abcdefg' SIMILAR 'a*#"%#"g*' ESCAPE '#') AS "abcdefg";
  abcdefg 
 ---------
  abcdefg
 (1 row)
 
 -- Vertical bar in any part affects only that part
-SELECT SUBSTRING('abcdefg' FROM 'a|b#"%#"g' FOR '#') AS "bcdef";
+SELECT SUBSTRING('abcdefg' SIMILAR 'a|b#"%#"g' ESCAPE '#') AS "bcdef";
  bcdef 
 -------
  bcdef
 (1 row)
 
-SELECT SUBSTRING('abcdefg' FROM 'a#"%#"x|g' FOR '#') AS "bcdef";
+SELECT SUBSTRING('abcdefg' SIMILAR 'a#"%#"x|g' ESCAPE '#') AS "bcdef";
  bcdef 
 -------
  bcdef
 (1 row)
 
-SELECT SUBSTRING('abcdefg' FROM 'a#"%|ab#"g' FOR '#') AS "bcdef";
+SELECT SUBSTRING('abcdefg' SIMILAR 'a#"%|ab#"g' ESCAPE '#') AS "bcdef";
  bcdef 
 -------
  bcdef
 (1 row)
 
 -- Can't have more than two part separators
-SELECT SUBSTRING('abcdefg' FROM 'a*#"%#"g*#"x' FOR '#') AS "error";
+SELECT SUBSTRING('abcdefg' SIMILAR 'a*#"%#"g*#"x' ESCAPE '#') AS "error";
 ERROR:  SQL regular expression may not contain more than two escape-double-quote separators
 CONTEXT:  SQL function "substring" statement 1
 -- Postgres extension: with 0 or 1 separator, assume parts 1 and 3 are empty
-SELECT SUBSTRING('abcdefg' FROM 'a#"%g' FOR '#') AS "bcdefg";
+SELECT SUBSTRING('abcdefg' SIMILAR 'a#"%g' ESCAPE '#') AS "bcdefg";
  bcdefg 
 --------
  bcdefg
 (1 row)
 
-SELECT SUBSTRING('abcdefg' FROM 'a%g' FOR '#') AS "abcdefg";
+SELECT SUBSTRING('abcdefg' SIMILAR 'a%g' ESCAPE '#') AS "abcdefg";
  abcdefg 
 ---------
  abcdefg
diff --git a/src/test/regress/sql/strings.sql b/src/test/regress/sql/strings.sql
index 3e89159a4f..14901a2692 100644
--- a/src/test/regress/sql/strings.sql
+++ b/src/test/regress/sql/strings.sql
@@ -132,31 +132,33 @@
 SELECT SUBSTRING('1234567890' FROM 4 FOR 3) = '456' AS "456";
 
 -- T581 regular expression substring (with SQL's bizarre regexp syntax)
+SELECT SUBSTRING('abcdefg' SIMILAR 'a#"(b_d)#"%' ESCAPE '#') AS "bcd";
+-- obsolete SQL99 syntax
 SELECT SUBSTRING('abcdefg' FROM 'a#"(b_d)#"%' FOR '#') AS "bcd";
 
 -- No match should return NULL
-SELECT SUBSTRING('abcdefg' FROM '#"(b_d)#"%' FOR '#') IS NULL AS "True";
+SELECT SUBSTRING('abcdefg' SIMILAR '#"(b_d)#"%' ESCAPE '#') IS NULL AS "True";
 
 -- Null inputs should return NULL
-SELECT SUBSTRING('abcdefg' FROM '%' FOR NULL) IS NULL AS "True";
-SELECT SUBSTRING(NULL FROM '%' FOR '#') IS NULL AS "True";
-SELECT SUBSTRING('abcdefg' FROM NULL FOR '#') IS NULL AS "True";
+SELECT SUBSTRING('abcdefg' SIMILAR '%' ESCAPE NULL) IS NULL AS "True";
+SELECT SUBSTRING(NULL SIMILAR '%' ESCAPE '#') IS NULL AS "True";
+SELECT SUBSTRING('abcdefg' SIMILAR NULL ESCAPE '#') IS NULL AS "True";
 
 -- The first and last parts should act non-greedy
-SELECT SUBSTRING('abcdefg' FROM 'a#"%#"g' FOR '#') AS "bcdef";
-SELECT SUBSTRING('abcdefg' FROM 'a*#"%#"g*' FOR '#') AS "abcdefg";
+SELECT SUBSTRING('abcdefg' SIMILAR 'a#"%#"g' ESCAPE '#') AS "bcdef";
+SELECT SUBSTRING('abcdefg' SIMILAR 'a*#"%#"g*' ESCAPE '#') AS "abcdefg";
 
 -- Vertical bar in any part affects only that part
-SELECT SUBSTRING('abcdefg' FROM 'a|b#"%#"g' FOR '#') AS "bcdef";
-SELECT SUBSTRING('abcdefg' FROM 'a#"%#"x|g' FOR '#') AS "bcdef";
-SELECT SUBSTRING('abcdefg' FROM 'a#"%|ab#"g' FOR '#') AS "bcdef";
+SELECT SUBSTRING('abcdefg' SIMILAR 'a|b#"%#"g' ESCAPE '#') AS "bcdef";
+SELECT SUBSTRING('abcdefg' SIMILAR 'a#"%#"x|g' ESCAPE '#') AS "bcdef";
+SELECT SUBSTRING('abcdefg' SIMILAR 'a#"%|ab#"g' ESCAPE '#') AS "bcdef";
 
 -- Can't have more than two part separators
-SELECT SUBSTRING('abcdefg' FROM 'a*#"%#"g*#"x' FOR '#') AS "error";
+SELECT SUBSTRING('abcdefg' SIMILAR 'a*#"%#"g*#"x' ESCAPE '#') AS "error";
 
 -- Postgres extension: with 0 or 1 separator, assume parts 1 and 3 are empty
-SELECT SUBSTRING('abcdefg' FROM 'a#"%g' FOR '#') AS "bcdefg";
-SELECT SUBSTRING('abcdefg' FROM 'a%g' FOR '#') AS "abcdefg";
+SELECT SUBSTRING('abcdefg' SIMILAR 'a#"%g' ESCAPE '#') AS "bcdefg";
+SELECT SUBSTRING('abcdefg' SIMILAR 'a%g' ESCAPE '#') AS "abcdefg";
 
 -- substring() with just two arguments is not allowed by SQL spec;
 -- we accept it, but we interpret the pattern as a POSIX regexp not SQL
-- 
2.27.0