*** a/doc/src/sgml/func.sgml
--- b/doc/src/sgml/func.sgml
***************
*** 8626,8631 **** SELECT xpath('/my:a/text()', '<my:a xmlns:my="http://example.com">test</my:a>',
--- 8626,8664 ----
  (1 row)
  ]]></screen>
     </para>
+    
+    <sect3>
+     <title>xpath_exists</title>
+     
+     <indexterm>
+      <primary>xpath_exists</primary>
+     </indexterm>
+     
+     <synopsis>
+      <function>xpath_exists</function>(<replaceable>xpath</replaceable>, <replaceable>xml</replaceable><optional>, <replaceable>nsarray</replaceable></optional>)
+     </synopsis>
+     
+     <para>
+      The function <function>xpath_exists</function> is a specialised form
+      of the <function>xpath</function> function. Though the functions are
+      syntactically the same the xpath expressions are evaluated in differing
+      contexts. Instead of returning the XML values that satisfy the xpath, this
+      function returns a boolean indicating whether the query was satisfied or not.
+     </para>
+     
+     <para>
+      Example:
+      <screen><![CDATA[
+ SELECT xpath_exists('/my:a/text()', '<my:a xmlns:my="http://example.com">test</my:a>', 
+                     ARRAY[ARRAY['my', 'http://example.com']]);
+ 
+  xpath_exists  
+ ------------
+  t
+ (1 row)
+ ]]></screen>
+     </para>
+    </sect3>
    </sect2>

    <sect2 id="functions-xml-mapping">
*** a/src/backend/utils/adt/xml.c
--- b/src/backend/utils/adt/xml.c
***************
*** 3495,3497 **** xpath(PG_FUNCTION_ARGS)
--- 3495,3681 ----
  	return 0;
  #endif
  }
+ 
+ /*
+  * Determines if the node specified by the supplied XPath exists
+  * in a given XML document, returning a boolean.
+  *
+  * It is up to the user to ensure that the XML passed is in fact
+  * an XML document - XPath doesn't work easily on fragments without
+  * a context node being known.
+  */
+ Datum
+ xpath_exists(PG_FUNCTION_ARGS)
+ {
+ #ifdef USE_LIBXML
+ 	text	   *xpath_expr_text = PG_GETARG_TEXT_P(0);
+ 	xmltype    *data = PG_GETARG_XML_P(1);
+ 	ArrayType  *namespaces = PG_GETARG_ARRAYTYPE_P(2);
+ 	ArrayBuildState *astate = NULL;
+ 	xmlParserCtxtPtr ctxt = NULL;
+ 	xmlDocPtr	doc = NULL;
+ 	xmlXPathContextPtr xpathctx = NULL;
+ 	xmlXPathCompExprPtr xpathcomp = NULL;
+ 	xmlXPathObjectPtr xpathobj = NULL;
+ 	char	   *datastr;
+ 	int32		len;
+ 	int32		xpath_len;
+ 	xmlChar    *string;
+ 	xmlChar    *xpath_expr;
+ 	int			i;
+ 	int			res_nitems;
+ 	int			ndim;
+ 	Datum	   *ns_names_uris;
+ 	bool	   *ns_names_uris_nulls;
+ 	int			ns_count;
+ 	int			result;
+ 
+ 	/*
+ 	 * Namespace mappings are passed as text[].  If an empty array is passed
+ 	 * (ndim = 0, "0-dimensional"), then there are no namespace mappings.
+ 	 * Else, a 2-dimensional array with length of the second axis being equal
+ 	 * to 2 should be passed, i.e., every subarray contains 2 elements, the
+ 	 * first element defining the name, the second one the URI.  Example:
+ 	 * ARRAY[ARRAY['myns', 'http://example.com'], ARRAY['myns2',
+ 	 * 'http://example2.com']].
+ 	 */
+ 	ndim = ARR_NDIM(namespaces);
+ 	if (ndim != 0)
+ 	{
+ 		int		   *dims;
+ 
+ 		dims = ARR_DIMS(namespaces);
+ 
+ 		if (ndim != 2 || dims[1] != 2)
+ 			ereport(ERROR,
+ 					(errcode(ERRCODE_DATA_EXCEPTION),
+ 					 errmsg("invalid array for XML namespace mapping"),
+ 					 errdetail("The array must be two-dimensional with length of the second axis equal to 2.")));
+ 
+ 		Assert(ARR_ELEMTYPE(namespaces) == TEXTOID);
+ 
+ 		deconstruct_array(namespaces, TEXTOID, -1, false, 'i',
+ 						  &ns_names_uris, &ns_names_uris_nulls,
+ 						  &ns_count);
+ 
+ 		Assert((ns_count % 2) == 0);	/* checked above */
+ 		ns_count /= 2;			/* count pairs only */
+ 	}
+ 	else
+ 	{
+ 		ns_names_uris = NULL;
+ 		ns_names_uris_nulls = NULL;
+ 		ns_count = 0;
+ 	}
+ 
+ 	datastr = VARDATA(data);
+ 	len = VARSIZE(data) - VARHDRSZ;
+ 	xpath_len = VARSIZE(xpath_expr_text) - VARHDRSZ;
+ 	if (xpath_len == 0)
+ 		ereport(ERROR,
+ 				(errcode(ERRCODE_DATA_EXCEPTION),
+ 				 errmsg("empty XPath expression")));
+ 
+ 	string = (xmlChar *) palloc((len + 1) * sizeof(xmlChar));
+ 	memcpy(string, datastr, len);
+ 	string[len] = '\0';
+ 
+ 	xpath_expr = (xmlChar *) palloc((xpath_len + 1) * sizeof(xmlChar));
+ 	memcpy(xpath_expr, VARDATA(xpath_expr_text), xpath_len);
+ 	xpath_expr[xpath_len] = '\0';
+ 
+ 	pg_xml_init();
+ 	xmlInitParser();
+ 
+ 	PG_TRY();
+ 	{
+ 		/*
+ 		 * redundant XML parsing (two parsings for the same value during one
+ 		 * command execution are possible)
+ 		 */
+ 		ctxt = xmlNewParserCtxt();
+ 		if (ctxt == NULL)
+ 			xml_ereport(ERROR, ERRCODE_OUT_OF_MEMORY,
+ 						"could not allocate parser context");
+ 		doc = xmlCtxtReadMemory(ctxt, (char *) string, len, NULL, NULL, 0);
+ 		if (doc == NULL)
+ 			xml_ereport(ERROR, ERRCODE_INVALID_XML_DOCUMENT,
+ 						"could not parse XML document");
+ 		xpathctx = xmlXPathNewContext(doc);
+ 		if (xpathctx == NULL)
+ 			xml_ereport(ERROR, ERRCODE_OUT_OF_MEMORY,
+ 						"could not allocate XPath context");
+ 		xpathctx->node = xmlDocGetRootElement(doc);
+ 		if (xpathctx->node == NULL)
+ 			xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
+ 						"could not find root XML element");
+ 
+ 		/* register namespaces, if any */
+ 		if (ns_count > 0)
+ 		{
+ 			for (i = 0; i < ns_count; i++)
+ 			{
+ 				char	   *ns_name;
+ 				char	   *ns_uri;
+ 
+ 				if (ns_names_uris_nulls[i * 2] ||
+ 					ns_names_uris_nulls[i * 2 + 1])
+ 					ereport(ERROR,
+ 							(errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
+ 					  errmsg("neither namespace name nor URI may be null")));
+ 				ns_name = TextDatumGetCString(ns_names_uris[i * 2]);
+ 				ns_uri = TextDatumGetCString(ns_names_uris[i * 2 + 1]);
+ 				if (xmlXPathRegisterNs(xpathctx,
+ 									   (xmlChar *) ns_name,
+ 									   (xmlChar *) ns_uri) != 0)
+ 					ereport(ERROR,		/* is this an internal error??? */
+ 							(errmsg("could not register XML namespace with name \"%s\" and URI \"%s\"",
+ 									ns_name, ns_uri)));
+ 			}
+ 		}
+ 
+ 		xpathcomp = xmlXPathCompile(xpath_expr);
+ 		if (xpathcomp == NULL)	/* TODO: show proper XPath error details */
+ 			xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
+ 						"invalid XPath expression");
+ 
+ 		/* Version 2.6.27 introduces a function named xmlXPathCompiledEvalToBoolean
+ 		 * however we can derive the existence by whether any nodes are returned
+ 		 * thereby preventing a library version upgrade */
+ 		xpathobj = xmlXPathCompiledEval(xpathcomp, xpathctx);
+ 		if (xpathobj == NULL)	/* TODO: reason? */
+ 			xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
+ 						"could not create XPath object");
+ 
+ 		if (xpathobj->nodesetval == NULL)
+ 			result = 0;
+ 		else
+ 			result = xpathobj->nodesetval->nodeNr;
+ 	}
+ 	PG_CATCH();
+ 	{
+ 		if (xpathobj)
+ 			xmlXPathFreeObject(xpathobj);
+ 		if (xpathcomp)
+ 			xmlXPathFreeCompExpr(xpathcomp);
+ 		if (xpathctx)
+ 			xmlXPathFreeContext(xpathctx);
+ 		if (doc)
+ 			xmlFreeDoc(doc);
+ 		if (ctxt)
+ 			xmlFreeParserCtxt(ctxt);
+ 		PG_RE_THROW();
+ 	}
+ 	PG_END_TRY();
+ 
+ 	xmlXPathFreeCompExpr(xpathcomp);
+ 	xmlXPathFreeContext(xpathctx);
+ 	xmlFreeDoc(doc);
+ 	xmlFreeParserCtxt(ctxt);
+ 
+ 	PG_RETURN_BOOL(result);
+ #else
+ 	NO_XML_SUPPORT();
+ 	return 0;
+ #endif
+ }
*** a/src/include/catalog/pg_proc.h
--- b/src/include/catalog/pg_proc.h
***************
*** 4385,4390 **** DESCR("evaluate XPath expression, with namespaces support");
--- 4385,4395 ----
  DATA(insert OID = 2932 (  xpath		 PGNSP PGUID 14 1 0 0 f f f t f i 2 0 143 "25 142" _null_ _null_ _null_ _null_ "select pg_catalog.xpath($1, $2, ''{}''::pg_catalog.text[])" _null_ _null_ _null_ ));
  DESCR("evaluate XPath expression");

+ DATA(insert OID = 3037 (  xpath_exists	 PGNSP PGUID 12 1 0 0 f f f t f i 3 0 16 "25 142 1009" _null_ _null_ _null_ _null_ xpath_exists _null_ _null_ _null_ ));
+ DESCR("evaluate XPath expression in a boolean context, with namespaces support");
+ DATA(insert OID = 3038 (  xpath_exists	 PGNSP PGUID 14 1 0 0 f f f t f i 2 0 16 "25 142" _null_ _null_ _null_ _null_ "select pg_catalog.xpath_exists($1, $2, ''{}''::pg_catalog.text[])" _null_ _null_ _null_ ));
+ DESCR("evaluate XPath expression in a boolean context");
+ 
  /* uuid */
  DATA(insert OID = 2952 (  uuid_in		   PGNSP PGUID 12 1 0 0 f f f t f i 1 0 2950 "2275" _null_ _null_ _null_ _null_ uuid_in _null_ _null_ _null_ ));
  DESCR("I/O");
*** a/src/include/utils/xml.h
--- b/src/include/utils/xml.h
***************
*** 37,42 **** extern Datum texttoxml(PG_FUNCTION_ARGS);
--- 37,43 ----
  extern Datum xmltotext(PG_FUNCTION_ARGS);
  extern Datum xmlvalidate(PG_FUNCTION_ARGS);
  extern Datum xpath(PG_FUNCTION_ARGS);
+ extern Datum xpath_exists(PG_FUNCTION_ARGS);

  extern Datum table_to_xml(PG_FUNCTION_ARGS);
  extern Datum query_to_xml(PG_FUNCTION_ARGS);
*** a/src/test/regress/expected/xml.out
--- b/src/test/regress/expected/xml.out
***************
*** 502,504 **** SELECT xpath('//b', '<a>one <b>two</b> three <b>etc</b></a>');
--- 502,557 ----
   {<b>two</b>,<b>etc</b>}
  (1 row)

+ -- Test xpath_exists evaluation
+ SELECT xpath_exists('//town[text() = ''Toronto'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
+  xpath_exists 
+ --------------
+  f
+ (1 row)
+ 
+ SELECT xpath_exists('//town[text() = ''Cwmbran'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
+  xpath_exists 
+ --------------
+  t
+ (1 row)
+ 
+ INSERT INTO xmltest VALUES (4, '<menu><beers><name>Budvar</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
+ INSERT INTO xmltest VALUES (5, '<menu><beers><name>Molson</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
+ INSERT INTO xmltest VALUES (6, '<myns:menu xmlns:myns="http://myns.com"><myns:beers><myns:name>Budvar</myns:name><myns:cost>free</myns:cost><myns:name>Carling</myns:name><myns:cost>lots</myns:cost></myns:beers></myns:menu>'::xml);
+ INSERT INTO xmltest VALUES (7, '<myns:menu xmlns:myns="http://myns.com"><myns:beers><myns:name>Molson</myns:name><myns:cost>free</myns:cost><myns:name>Carling</myns:name><myns:cost>lots</myns:cost></myns:beers></myns:menu>'::xml);
+ SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/menu/beer',data);
+  count 
+ -------
+      0
+ (1 row)
+ 
+ SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/menu/beers',data);
+  count 
+ -------
+      2
+ (1 row)
+ 
+ SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/menu/beers/name[text() = ''Molson'']',data);
+  count 
+ -------
+      1
+ (1 row)
+ 
+ SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/myns:menu/myns:beer',data,ARRAY[ARRAY['myns','http://myns.com']]);
+  count 
+ -------
+      0
+ (1 row)
+ 
+ SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/myns:menu/myns:beers',data,ARRAY[ARRAY['myns','http://myns.com']]);
+  count 
+ -------
+      2
+ (1 row)
+ 
+ SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/myns:menu/myns:beers/myns:name[text() = ''Molson'']',data,ARRAY[ARRAY['myns','http://myns.com']]);
+  count 
+ -------
+      1
+ (1 row)
+ 
*** a/src/test/regress/sql/xml.sql
--- b/src/test/regress/sql/xml.sql
***************
*** 163,165 **** SELECT xpath('', '');
--- 163,181 ----
  SELECT xpath('//text()', '<local:data xmlns:local="http://127.0.0.1"><local:piece id="1">number one</local:piece><local:piece id="2" /></local:data>');
  SELECT xpath('//loc:piece/@id', '<local:data xmlns:local="http://127.0.0.1"><local:piece id="1">number one</local:piece><local:piece id="2" /></local:data>', ARRAY[ARRAY['loc', 'http://127.0.0.1']]);
  SELECT xpath('//b', '<a>one <b>two</b> three <b>etc</b></a>');
+ 
+ -- Test xpath_exists evaluation
+ SELECT xpath_exists('//town[text() = ''Toronto'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
+ SELECT xpath_exists('//town[text() = ''Cwmbran'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
+ 
+ INSERT INTO xmltest VALUES (4, '<menu><beers><name>Budvar</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
+ INSERT INTO xmltest VALUES (5, '<menu><beers><name>Molson</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
+ INSERT INTO xmltest VALUES (6, '<myns:menu xmlns:myns="http://myns.com"><myns:beers><myns:name>Budvar</myns:name><myns:cost>free</myns:cost><myns:name>Carling</myns:name><myns:cost>lots</myns:cost></myns:beers></myns:menu>'::xml);
+ INSERT INTO xmltest VALUES (7, '<myns:menu xmlns:myns="http://myns.com"><myns:beers><myns:name>Molson</myns:name><myns:cost>free</myns:cost><myns:name>Carling</myns:name><myns:cost>lots</myns:cost></myns:beers></myns:menu>'::xml);
+ 
+ SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/menu/beer',data);
+ SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/menu/beers',data);
+ SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/menu/beers/name[text() = ''Molson'']',data);
+ SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/myns:menu/myns:beer',data,ARRAY[ARRAY['myns','http://myns.com']]);
+ SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/myns:menu/myns:beers',data,ARRAY[ARRAY['myns','http://myns.com']]);
+ SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/myns:menu/myns:beers/myns:name[text() = ''Molson'']',data,ARRAY[ARRAY['myns','http://myns.com']]);