Fix for BUG#10151: In Item_func_case::find_item don't assume that parameter...

Fix for BUG#10151: In Item_func_case::find_item don't assume that parameter str != &(this->str_value)

mysql-test/r/case.result

@@ -154,3 +154,18 @@ t1	CREATE TABLE `t1` (
   `COALESCE('a' COLLATE latin1_bin,'b')` char(1) character set latin1 collate latin1_bin NOT NULL default ''
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 DROP TABLE t1;
+SELECT 'case+union+test'
+UNION 
+SELECT CASE LOWER('1') WHEN LOWER('2') THEN 'BUG' ELSE 'nobug' END;
+case+union+test
+case+union+test
+nobug
+SELECT CASE LOWER('1') WHEN LOWER('2') THEN 'BUG' ELSE 'nobug' END;
+CASE LOWER('1') WHEN LOWER('2') THEN 'BUG' ELSE 'nobug' END
+nobug
+SELECT 'case+union+test'
+UNION 
+SELECT CASE '1' WHEN '2' THEN 'BUG' ELSE 'nobug' END;
+case+union+test
+case+union+test
+nobug

mysql-test/t/case.test

@@ -107,3 +107,14 @@ explain extended SELECT
  COALESCE('a' COLLATE latin1_bin,'b');
 SHOW CREATE TABLE t1;
 DROP TABLE t1;
+
+# Test for BUG#10151
+SELECT 'case+union+test'
+UNION 
+SELECT CASE LOWER('1') WHEN LOWER('2') THEN 'BUG' ELSE 'nobug' END;
+
+SELECT CASE LOWER('1') WHEN LOWER('2') THEN 'BUG' ELSE 'nobug' END;
+
+SELECT 'case+union+test'
+UNION 
+SELECT CASE '1' WHEN '2' THEN 'BUG' ELSE 'nobug' END;

sql/item_cmpfunc.cc

@@ -1174,6 +1174,8 @@ Item *Item_func_case::find_item(String *str)
   String *first_expr_str,*tmp;
   longlong first_expr_int;
   double   first_expr_real;
+  char buff[MAX_FIELD_WIDTH];
+  String buff_str(buff,sizeof(buff),default_charset());
   
   /* These will be initialized later */
   LINT_INIT(first_expr_str);
@@ -1186,7 +1188,7 @@ Item *Item_func_case::find_item(String *str)
     {
       case STRING_RESULT:
       	// We can't use 'str' here as this may be overwritten
-	if (!(first_expr_str= args[first_expr_num]->val_str(&str_value)))
+	if (!(first_expr_str= args[first_expr_num]->val_str(&buff_str)))
 	  return else_expr_num != -1 ? args[else_expr_num] : 0;	// Impossible
         break;
       case INT_RESULT: