How to create index on xmtype column

Question

Hi,
I have a table as follows
CREATE TABLE T_TEST_XML (PROCESS_ID NUMBER, TXT_XML XMLTYPE);
I query the above table very frequently with the query
SELECT * FROM T_TEST_XML TXS WHERE EXISTSNODE(TXS.TXT_XML, '/order[status="PEN"]') = 1
How to create function based index on the TXT_XML column for the xpath expression /order[status="PEN"]' to improve the query performance?
Thank you

Answer 1

Actually if you are limited to using older software
1. Consider defining an XML Schema and storing the XML using object relational storage.
or
2. If you must store the XML as CLOB create the index on extractValue(), rather than existsNode() and supply the predicate value at the SQL level rather than the XPATH level.
SQL> DROP TABLE T_TEST_XML
  2  /
Table dropped.
SQL> CREATE TABLE T_TEST_XML (PROCESS_ID NUMBER, TXT_XML XMLTYPE)
  2  /
Table created.
SQL> create INDEX T_TEXT_XML_IDX on T_TEST_XML( extractValue(TXT_XML,'/order/status'))
  2  /
Index created.
SQL> set autotrace on explain
SQL> --
SQL> SELECT *
  2    FROM T_TEST_XML TXS
  3   WHERE ExistsNode(TXT_XML,'/order[status="PEN"]') = 1
  4  /
no rows selected
Execution Plan
Plan hash value: 3001212210
| Id  | Operation          | Name       | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT   |            |     1 |  2017 |    31   (0)| 00:00:01 |
|   1 |  NESTED LOOPS SEMI |            |     1 |  2017 |    31   (0)| 00:00:01 |
|   2 |   TABLE ACCESS FULL| T_TEST_XML |     1 |  2015 |     2   (0)| 00:00:01 |
|*  3 |   XPATH EVALUATION |            |       |       |            |          |
Predicate Information (identified by operation id):
   3 - filter("P"."C_01$"='PEN')
Note
   - dynamic sampling used for this statement (level=2)
SQL> SELECT *
  2    FROM T_TEST_XML TXS
  3   WHERE extractValue(TXT_XML,'/order/status') = 'PEN'
  4  /
no rows selected
Execution Plan
Plan hash value: 1430727070
| Id  | Operation                   | Name           | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT            |                |     1 |  2015 |     1   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| T_TEST_XML     |     1 |  2015 |     1   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | T_TEXT_XML_IDX |     1 |       |     1   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   2 - access(EXTRACTVALUE(SYS_MAKEXML(0,"SYS_NC00003$"),'/order/status',null,0,0,5242
              93,133120)='PEN')
Note
   - dynamic sampling used for this statement (level=2)
SQL>
SQL>
SQL>
SQL>
SQL>
SQL>This allows the index to support querying on any value of status, rather than just PEN