Bug#43183 ExctractValue() brings result list in missorder

The problem is that XML functions(items) do not reset null_value
before their execution and further item excution may use
null_value value of the previous result.
The fix is to reset null_value.

mysql-test/r/xml.result

@@ -1064,4 +1064,33 @@ select extractvalue('<a></a>','"b"/a');
 ERROR HY000: XPATH syntax error: '/a'
 select extractvalue('<a></a>','(1)/a');
 ERROR HY000: XPATH syntax error: '/a'
+CREATE TABLE IF NOT EXISTS t1 (
+id int(10) unsigned NOT NULL AUTO_INCREMENT,
+xml text,
+PRIMARY KEY (id)
+) ENGINE=MyISAM;
+INSERT INTO t1 (id, xml) VALUES
+(15, '<?xml version="1.0"?><bla name="blubb"></bla>'),
+(14, '<xml version="kaputt">');
+SELECT
+extractvalue( xml, '/bla/@name' ),
+extractvalue( xml, '/bla/@name' )
+FROM t1 ORDER BY t1.id;
+extractvalue( xml, '/bla/@name' )	extractvalue( xml, '/bla/@name' )
+NULL	NULL
+blubb	blubb
+Warnings:
+Warning	1525	Incorrect XML value: 'parse error at line 1 pos 23: unexpected END-OF-INPUT'
+Warning	1525	Incorrect XML value: 'parse error at line 1 pos 23: unexpected END-OF-INPUT'
+SELECT
+UpdateXML(xml, '/bla/@name', 'test'),
+UpdateXML(xml, '/bla/@name', 'test')
+FROM t1 ORDER BY t1.id;
+UpdateXML(xml, '/bla/@name', 'test')	UpdateXML(xml, '/bla/@name', 'test')
+NULL	NULL
+<?xml version="1.0"?><bla test></bla>	<?xml version="1.0"?><bla test></bla>
+Warnings:
+Warning	1525	Incorrect XML value: 'parse error at line 1 pos 23: unexpected END-OF-INPUT'
+Warning	1525	Incorrect XML value: 'parse error at line 1 pos 23: unexpected END-OF-INPUT'
+DROP TABLE t1;
 End of 5.1 tests

mysql-test/t/xml.test

@@ -590,4 +590,31 @@ select extractvalue('<a></a>','"b"/a');
 --error ER_UNKNOWN_ERROR
 select extractvalue('<a></a>','(1)/a');
 
+#
+# Bug#43183 ExctractValue() brings result list in missorder
+#
+CREATE TABLE IF NOT EXISTS t1 (
+  id int(10) unsigned NOT NULL AUTO_INCREMENT,
+  xml text,
+  PRIMARY KEY (id)
+) ENGINE=MyISAM;
+
+INSERT INTO t1 (id, xml) VALUES
+(15, '<?xml version="1.0"?><bla name="blubb"></bla>'),
+(14, '<xml version="kaputt">');
+
+
+SELECT
+extractvalue( xml, '/bla/@name' ),
+extractvalue( xml, '/bla/@name' )
+FROM t1 ORDER BY t1.id;
+
+
+SELECT
+UpdateXML(xml, '/bla/@name', 'test'),
+UpdateXML(xml, '/bla/@name', 'test')
+FROM t1 ORDER BY t1.id;
+
+DROP TABLE t1;
+
 --echo End of 5.1 tests

sql/item_xmlfunc.cc

@@ -2785,6 +2785,7 @@ String *Item_xml_str_func::parse_xml(String *raw_xml, String *parsed_xml_buf)
 String *Item_func_xml_extractvalue::val_str(String *str)
 {
   String *res;
+  null_value= 0;
   if (!nodeset_func ||
       !(res= args[0]->val_str(str)) || 
       !parse_xml(res, &pxml))
@@ -2801,6 +2802,7 @@ String *Item_func_xml_update::val_str(String *str)
 {
   String *res, *nodeset, *rep;
 
+  null_value= 0;
   if (!nodeset_func || 
       !(res= args[0]->val_str(str)) ||
       !(rep= args[2]->val_str(&tmp_value3)) ||