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Fix the BY {REF,VALUE} clause of XMLEXISTS/XMLTABLE
This clause is used to indicate the passing mode of a XML document, but we were doing it wrong: we accepted BY REF and ignored it, and rejected BY VALUE as a syntax error. The reality, however, is that documents are always passed BY VALUE, so rejecting that clause was silly. Change things so that we accept BY VALUE. BY REF continues to be accepted, and continues to be ignored. Author: Chapman Flack Reviewed-by: Pavel Stehule Discussion: https://postgr.es/m/5C297BB7.9070509@anastigmatix.net
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‎doc/src/sgml/func.sgml

+25-14
Original file line numberDiff line numberDiff line change
@@ -10583,7 +10583,7 @@ SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab;
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</indexterm>
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<synopsis>
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<function>XMLEXISTS</function>(<replaceable>text</replaceable> PASSING <optional>BY REF</optional> <replaceable>xml</replaceable> <optional>BY REF</optional>)
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<function>XMLEXISTS</function>(<replaceable>text</replaceable> PASSING <optional>BY { REF | VALUE }</optional> <replaceable>xml</replaceable> <optional>BY { REF | VALUE }</optional>)
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</synopsis>
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<para>
@@ -10596,7 +10596,7 @@ SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab;
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<para>
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Example:
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<screen><![CDATA[
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SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY REF '<towns><town>Toronto</town><town>Ottawa</town></towns>');
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SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY VALUE '<towns><town>Toronto</town><town>Ottawa</town></towns>');
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xmlexists
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------------
@@ -10606,14 +10606,25 @@ SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY REF '<towns><town>Tor
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</para>
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<para>
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The <literal>BY REF</literal> clauses have no effect in
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PostgreSQL, but are allowed for SQL conformance and compatibility
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with other implementations. Per SQL standard, the
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first <literal>BY REF</literal> is required, the second is
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optional. Also note that the SQL standard specifies
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the <function>xmlexists</function> construct to take an XQuery
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expression as first argument, but PostgreSQL currently only
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supports XPath, which is a subset of XQuery.
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The <literal>BY REF</literal> or <literal>BY VALUE</literal> clauses
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have no effect in <productname>PostgreSQL<productname>, but are allowed
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for compatibility with other implementations. Per the <acronym>SQL</acronym>
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standard, the one that precedes any argument is required, and indicates
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the default for arguments that follow, and one may follow any argument to
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override the default.
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<productname>PostgreSQL</productname> ignores <literal>BY REF</literal>
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and passes by value always.
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</para>
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<para>
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In the <acronym>SQL</acronym> standard, an <function>xmlexists</function>
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construct evaluates an expression in the XQuery language, allows passing
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values for named parameters in the expression as well as for the context
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item, and does not require the passed values to be documents, or even of
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XML type.
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In <productname>PostgreSQL</productname>, this construct currently only
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evaluates an XPath 1.0 expression, and allows passing only one value,
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which must be an XML document, to be the context item.
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</para>
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</sect3>
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@@ -10820,7 +10831,7 @@ SELECT xpath_exists('/my:a/text()', '<my:a xmlns:my="http://example.com">test</m
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<synopsis>
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<function>xmltable</function>( <optional>XMLNAMESPACES(<replaceable>namespace uri</replaceable> AS <replaceable>namespace name</replaceable><optional>, ...</optional>), </optional>
10823-
<replaceable>row_expression</replaceable> PASSING <optional>BY REF</optional> <replaceable>document_expression</replaceable> <optional>BY REF</optional>
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<replaceable>row_expression</replaceable> PASSING <optional>BY { REF | VALUE }</optional> <replaceable>document_expression</replaceable> <optional>BY { REF | VALUE }</optional>
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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>
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| FOR ORDINALITY }
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<optional>, ...</optional>
@@ -10850,11 +10861,11 @@ SELECT xpath_exists('/my:a/text()', '<my:a xmlns:my="http://example.com">test</m
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<para>
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<replaceable>document_expression</replaceable> provides the XML document to
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operate on.
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The <literal>BY REF</literal> clauses have no effect in PostgreSQL,
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but are allowed for SQL conformance and compatibility with other
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implementations.
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The argument must be a well-formed XML document; fragments/forests
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are not accepted.
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The <literal>BY REF</literal> or <literal>BY VALUE</literal> clauses are
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accepted, as described for the <function>xmlexists</function> predicate,
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but ignored; PostgreSQL currently passes XML by value always.
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</para>
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<para>

‎src/backend/catalog/sql_features.txt

+2-2
Original file line numberDiff line numberDiff line change
@@ -635,8 +635,8 @@ X204 XMLQuery: initializing an XQuery variable NO
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X205 XMLQuery: EMPTY ON EMPTY option NO
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X206 XMLQuery: NULL ON EMPTY option NO
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X211 XML 1.1 support NO
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X221 XML passing mechanism BY VALUE NO
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X222 XML passing mechanism BY REF YES
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X221 XML passing mechanism BY VALUE YES
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X222 XML passing mechanism BY REF NO parser accepts BY REF but ignores it; passing is always BY VALUE
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X231 XML(CONTENT(UNTYPED)) type NO
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X232 XML(CONTENT(ANY)) type NO
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X241 RETURNING CONTENT in XML publishing NO

‎src/backend/parser/gram.y

+10-5
Original file line numberDiff line numberDiff line change
@@ -13951,20 +13951,25 @@ xmlexists_argument:
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{
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$$ = $2;
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}
13954-
| PASSING c_expr BY REF
13954+
| PASSING c_expr xml_passing_mech
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{
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$$ = $2;
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}
13958-
| PASSING BY REF c_expr
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| PASSING xml_passing_mech c_expr
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{
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$$ = $4;
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$$ = $3;
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}
13962-
| PASSING BY REF c_expr BY REF
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| PASSING xml_passing_mech c_expr xml_passing_mech
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{
13964-
$$ = $4;
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$$ = $3;
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}
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;
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xml_passing_mech:
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BY REF
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| BY VALUE_P
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;
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/*
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* Aggregate decoration clauses

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