Parsing XML attributes

Question

Hi.
I have the following example of XML structure :
create table xxx (xmlval xmltype);
insert into xxx values (xmltype('<?xml version="1.0" encoding="utf-8"?> <Records> <Card P1="10" P2="20" /> </Records>'));
I have written the following code :
declare
lx_xml_node xmltype;
l_str varchar2(100);
begin
select e.xmlval.extract('/Records/Card[1]') into lx_xml_node from xxx e;
select lx_xml_node.extract('/@Card/P1').getStringVal() into l_str from xxx e;
dbms_output.put_line(l_str);
end;
The problem is I cant get the value of P1 attibute (l_str IS NULL). Is there a way to extract P1 and P2 attribute from xml node? Any help or hint appreciated.
Thanks.

Answer 1

From your first post, I thought you were querying directly from the XMLType column.
If you're transferring the data to the PL/SQL engine then you immediately disable all possible optimizations, as Jason (A_Non) explained above.
Also note that in the query you gave, you're performing a cartesian join.
Since you're on 11.2, I think you should try out binary XML storage and measure the difference (it should be huge).
Here's a test case on a document containing 1000 Node3 :
SQL> drop table tmp_xml purge;
Table dropped.
SQL> create table tmp_xml of xmltype
  2  xmltype store as securefile binary xml;
Table created.
SQL> insert into tmp_xml values(xmltype(bfilename('XML_DIR','sample.xml'),nls_charset_id('AL32UTF8')));
1 row created.
SQL> commit;
Commit complete.
SQL> exec dbms_stats.gather_table_stats(user, 'TMP_XML');
PL/SQL procedure successfully completed.
SQL> select count(*)
  2  from tmp_xml t
  3     , xmltable('/Node1/Node2/Node3' passing t.object_value) x
  4  ;
  COUNT(*)
      1000
SQL> set timing on
SQL> set autotrace traceonly
SQL> SELECT t_hdr.h1,
  2         t_hdr.h2,
  3         t_hdr.h3,
  4         t_hdr.h4,
  5         t_hdr.h5,
  6         t_hdr.h6,
  7         t_hdr.h7,
  8         t_rec.*
  9  FROM tmp_xml t
10     , XMLTable('/Node1'
11        passing t.object_value
12        columns
13          h1    VARCHAR2(5)  path 'h1',
14          h2    VARCHAR2(14) path 'h2',
15          h3    VARCHAR2(14) path 'h3',
16          h4    VARCHAR2(14) path 'h4',
17          h5    VARCHAR2(14) path 'h5',
18          h6    VARCHAR2(50) path 'h6',
19          h7    VARCHAR2(14) path 'h7',
20          Node2 XMLType      path 'Node2'
21       ) t_hdr
22     , XMLTable('/Node2/Node3'
23        passing t_hdr.Node2
24        columns
25          rc1  VARCHAR2(21) path '@rc1',
26          rc2  VARCHAR2(5)  path '@rc2',
27          rc3  VARCHAR2(17) path '@rc3',
28          rc4  VARCHAR2(17) path '@rc4',
29          rc5  VARCHAR2(17) path '@rc5',
30          rc6  VARCHAR2(17) path '@rc6',
31          rc7  VARCHAR2(5)  path '@rc7',
32          rc8  VARCHAR2(12) path '@rc8',
33          rc9  VARCHAR2(12) path '@rc9',
34          rc10 VARCHAR2(32) path '@rc10',
35          rc11 VARCHAR2(32) path '@rc11',
36          rc12 VARCHAR2(32) path '@rc12',
37          rc13 VARCHAR2(5)  path '@rc13',
38          rc14 VARCHAR2(7)  path '@rc14',
39          rc15 VARCHAR2(32) path '@rc15',
40          rc16 VARCHAR2(29) path '@rc16',
41          rc17 VARCHAR2(4)  path '@rc17',
42          rc18 VARCHAR2(6)  path '@rc18',
43          rc19 VARCHAR2(11) path '@rc19',
44          rc20 VARCHAR2(11) path '@rc20',
45          rc21 VARCHAR2(13) path '@rc21',
46          rc22 VARCHAR2(12) path '@rc22',
47          rc23 VARCHAR2(5)  path '@rc23',
48          rc24 VARCHAR2(4)  path '@rc24',
49          rc25 VARCHAR2(17) path '@rc25',
50          rc26 VARCHAR2(14) path '@rc26',
51          rc27 VARCHAR2(3)  path '@rc27',
52          rc28 VARCHAR2(3)  path '@rc28',
53          rc29 VARCHAR2(17) path '@rc29',
54          rc30 VARCHAR2(5)  path '@rc30',
55          rc31 VARCHAR2(11) path '@rc31',
56          rc32 VARCHAR2(11) path '@rc32',
57          rc33 VARCHAR2(11) path '@rc33',
58          rc34 VARCHAR2(11) path '@rc34',
59          rc35 VARCHAR2(11) path '@rc35',
60          rc36 VARCHAR2(11) path '@rc36',
61          rc37 VARCHAR2(11) path '@rc37',
62          rc38 VARCHAR2(11) path '@rc38',
63          rc39 VARCHAR2(11) path '@rc39',
64          rc40 VARCHAR2(11) path '@rc40',
65          rc41 VARCHAR2(11) path '@rc41',
66          rc42 VARCHAR2(11) path '@rc42',
67          rc43 VARCHAR2(11) path '@rc43',
68          rc44 VARCHAR2(11) path '@rc44',
69          rc45 VARCHAR2(11) path '@rc45',
70          rc46 VARCHAR2(11) path '@rc46'
71       ) t_rec
72  ;
1000 rows selected.
Elapsed: 00:00:01.22
Execution Plan
Plan hash value: 2982218919
| Id  | Operation           | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT    |         |    66M|    11G|   222K  (1)| 00:44:29 |
|   1 |  NESTED LOOPS       |         |    66M|    11G|   222K  (1)| 00:44:29 |
|   2 |   NESTED LOOPS      |         |  8168 |  1427K|    32   (0)| 00:00:01 |
|   3 |    TABLE ACCESS FULL| TMP_XML |     1 |    87 |     3   (0)| 00:00:01 |
|   4 |    XPATH EVALUATION |         |       |       |            |          |
|   5 |   XPATH EVALUATION  |         |       |       |            |          |
Statistics
          8  recursive calls
          0  db block gets
       8791  consistent gets
          0  physical reads
          0  redo size
      23347  bytes sent via SQL*Net to client
       1145  bytes received via SQL*Net from client
         68  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
       1000  rows processed