基於xml屬性的Oracle xmltype列索引

Question

我正在爲xmltype列使用結構化存儲類型。我試圖創建一個屬性的索引，但不知何故Oracle不採取索引和做全表掃描。我已經檢查了文檔http://docs.oracle.com/cd/B28359_01/appdev.111/b28369/xdb_indexing.htm#CHDCJIJB，但它沒有舉例說明在屬性上創建索引。 有人可以給我一個在屬性上創建xml索引的例子嗎？

感謝 凱文

Answer 1

你需要在這裏展示一些代碼。

以下是創建一個屬性的xmlindex（及其子節點）的例子：

SQL> create table xmltest (a xmltype); 

Table created. 

SQL> insert into xmltest values ('<root> 
    2 <a test="foo" test2="asd"> 
    3  <b>hi</b> 
    4 </a> 
    5 <a test="foo2" test2="asd2">hi</a> 
    6 </root>'); 

1 row created. 

SQL> commit; 

Commit complete. 

SQL> create index test_xmlindex on xmltest (a) 
    2 indextype is XDB.XMLIndex 
    3 parameters ('paths (include (/root/a/@test))'); 

Index created. 

SQL> set pagesize 100 lines 200 heading off 
SQL> explain plan for select * from xmltest where xmlexists('/root/a[@test="foo"]' passing a); 

Explained. 

SQL> select * from table(dbms_xplan.display()); 

Plan hash value: 2925043098 

------------------------------------------------------------------------------------------------------------------- 
| Id | Operation      | Name       | Rows | Bytes | Cost (%CPU)| Time  | 
------------------------------------------------------------------------------------------------------------------- 
| 0 | SELECT STATEMENT     |        |  1 | 2026 |  6 (17)| 00:00:01 | 
| 1 | NESTED LOOPS     |        |  1 | 2026 |  6 (17)| 00:00:01 | 
| 2 | VIEW       | VW_SQ_1      |  1 | 12 |  4 (0)| 00:00:01 | 
| 3 | HASH UNIQUE     |        |  1 | 5046 |   |   | 
| 4 |  NESTED LOOPS     |        |  |  |   |   | 
| 5 |  NESTED LOOPS    |        |  1 | 5046 |  4 (0)| 00:00:01 | 
|* 6 |  TABLE ACCESS BY INDEX ROWID| SYS82641_TEST_XMLIN_PATH_TABLE |  1 | 3524 |  2 (0)| 00:00:01 | 
|* 7 |  INDEX RANGE SCAN   | SYS82641_TEST_XMLIN_VALUE_IX |  1 |  |  1 (0)| 00:00:01 | 
|* 8 |  INDEX RANGE SCAN   | SYS82641_TEST_XMLIN_PIKEY_IX |  1 |  |  1 (0)| 00:00:01 | 
|* 9 |  TABLE ACCESS BY INDEX ROWID | SYS82641_TEST_XMLIN_PATH_TABLE |  1 | 1522 |  2 (0)| 00:00:01 | 
| 10 | TABLE ACCESS BY USER ROWID  | XMLTEST      |  1 | 2014 |  1 (0)| 00:00:01 | 
------------------------------------------------------------------------------------------------------------------- 

通過索引paths (include (/root/a/@test))它將包含在索引中的孩子<b>節點，但不是test2屬性。如果省略/@test，則索引也會獲得test2屬性。