xmltable-xmlexists-passing-mechanisms-1.patch

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 06f3f69..df0fe4d 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -10583,7 +10583,7 @@ SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab;
     </indexterm>
 
 <synopsis>
-<function>XMLEXISTS</function>(<replaceable>text</replaceable> PASSING <optional>BY REF</optional> <replaceable>xml</replaceable> <optional>BY REF</optional>)
+<function>XMLEXISTS</function>(<replaceable>text</replaceable> PASSING <optional>BY { REF | VALUE }</optional> <replaceable>xml</replaceable> <optional>BY { REF | VALUE }</optional>)
 </synopsis>
 
     <para>
@@ -10596,7 +10596,7 @@ SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab;
     <para>
      Example:
      <screen><![CDATA[
-SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY REF '<towns><town>Toronto</town><town>Ottawa</town></towns>');
+SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY VALUE '<towns><town>Toronto</town><town>Ottawa</town></towns>');
 
  xmlexists
 ------------
@@ -10606,14 +10606,22 @@ SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY REF '<towns><town>Tor
     </para>
 
     <para>
-     The <literal>BY REF</literal> clauses have no effect in
-     PostgreSQL, but are allowed for SQL conformance and compatibility
-     with other implementations.  Per SQL standard, the
-     first <literal>BY REF</literal> is required, the second is
-     optional.  Also note that the SQL standard specifies
-     the <function>xmlexists</function> construct to take an XQuery
-     expression as first argument, but PostgreSQL currently only
-     supports XPath, which is a subset of XQuery.
+     The <literal>BY REF</literal> or <literal>BY VALUE</literal> clauses
+     have no effect in PostgreSQL, but are allowed for compatibility
+     with other implementations.  Per SQL standard, the one that precedes
+     any argument is required, and indicates the default for arguments that
+     follow, and one may follow any argument to override the default.
+     PostgreSQL ignores <literal>BY REF</literal> and passes by value always.
+    </para>
+
+    <para>
+     In the SQL standard, an <function>xmlexists</function> construct first
+     appears in SQL:2006, evaluates an expression in the XML Query language,
+     allows passing values for named parameters in the expression as well
+     as for the context item, and does not require the passed values to be
+     documents, or even of XML type. In PostgreSQL, this construct currently
+     only evaluates an XPath 1.0 expression, and allows passing only one value,
+     which must be an XML document, to be the context item.  
     </para>
    </sect3>
 
@@ -10820,7 +10828,7 @@ SELECT xpath_exists('/my:a/text()', '<my:a xmlns:my="http://example.com">test</m
 
 <synopsis>
 <function>xmltable</function>( <optional>XMLNAMESPACES(<replaceable>namespace uri</replaceable> AS <replaceable>namespace name</replaceable><optional>, ...</optional>), </optional>
-          <replaceable>row_expression</replaceable> PASSING <optional>BY REF</optional> <replaceable>document_expression</replaceable> <optional>BY REF</optional>
+          <replaceable>row_expression</replaceable> PASSING <optional>BY { REF | VALUE }</optional> <replaceable>document_expression</replaceable> <optional>BY { REF | VALUE }</optional>
           COLUMNS <replaceable>name</replaceable> { <replaceable>type</replaceable> <optional>PATH <replaceable>column_expression</replaceable></optional> <optional>DEFAULT <replaceable>default_expression</replaceable></optional> <optional>NOT NULL | NULL</optional>
                         | FOR ORDINALITY }
                    <optional>, ...</optional>
@@ -10850,11 +10858,11 @@ SELECT xpath_exists('/my:a/text()', '<my:a xmlns:my="http://example.com">test</m
     <para>
      <replaceable>document_expression</replaceable> provides the XML document to
      operate on.
-     The <literal>BY REF</literal> clauses have no effect in PostgreSQL,
-     but are allowed for SQL conformance and compatibility with other
-     implementations.
      The argument must be a well-formed XML document; fragments/forests
      are not accepted.
+     The <literal>BY REF</literal> or <literal>BY VALUE</literal> clauses are
+     accepted, as described for the <function>xmlexists</function> predicate,
+     but ignored; PostgreSQL currently passes XML by value always.
     </para>
 
     <para>
diff --git a/src/backend/catalog/sql_features.txt b/src/backend/catalog/sql_features.txt
index aeb262a..bade0fe 100644
--- a/src/backend/catalog/sql_features.txt
+++ b/src/backend/catalog/sql_features.txt
@@ -635,8 +635,8 @@ X204	XMLQuery: initializing an XQuery variable			NO
 X205	XMLQuery: EMPTY ON EMPTY option			NO	
 X206	XMLQuery: NULL ON EMPTY option			NO	
 X211	XML 1.1 support			NO	
-X221	XML passing mechanism BY VALUE			NO	
-X222	XML passing mechanism BY REF			YES	
+X221	XML passing mechanism BY VALUE			YES	
+X222	XML passing mechanism BY REF			NO	parser accepts BY REF but ignores it; passing is always BY VALUE
 X231	XML(CONTENT(UNTYPED)) type			NO	
 X232	XML(CONTENT(ANY)) type			NO	
 X241	RETURNING CONTENT in XML publishing			NO	
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index c086235..1b303d7 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -13942,20 +13942,25 @@ xmlexists_argument:
 				{
 					$$ = $2;
 				}
-			| PASSING c_expr BY REF
+			| PASSING c_expr xml_passing_mech
 				{
 					$$ = $2;
 				}
-			| PASSING BY REF c_expr
+			| PASSING xml_passing_mech c_expr
 				{
-					$$ = $4;
+					$$ = $3;
 				}
-			| PASSING BY REF c_expr BY REF
+			| PASSING xml_passing_mech c_expr xml_passing_mech
 				{
-					$$ = $4;
+					$$ = $3;
 				}
 		;
 
+xml_passing_mech:
+			BY REF
+			| BY VALUE_P
+		;
+
 
 /*
  * Aggregate decoration clauses