我可以在Oracle 11(请参阅SQL Fiddle)和Oracle 12中重现以下行为。
CREATE TYPE my_tab IS TABLE OF NUMBER(3);
CREATE TABLE test AS SELECT ROWNUM AS id FROM dual CONNECT BY ROWNUM <= 1000;
CREATE UNIQUE INDEX idx_test ON test( id );
CREATE VIEW my_view AS
SELECT id, COUNT(1) OVER ( PARTITION BY id ) AS cnt
FROM test;
以下情况按预期使用索引:
SELECT * FROM my_view
WHERE id IN ( 1, 2 );
---------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2 | 52 | 2 (0)| 00:00:01 |
| 1 | VIEW | MY_VIEW | 2 | 52 | 2 (0)| 00:00:01 |
| 2 | WINDOW BUFFER | | 2 | 8 | 2 (0)| 00:00:01 |
| 3 | INLIST ITERATOR | | | | | |
|* 4 | INDEX UNIQUE SCAN| IDX_TEST | 2 | 8 | 2 (0)| 00:00:01 |
---------------------------------------------------------------------------------
即使提供了基数提示，以下情况也不使用索引:
SELECT * FROM my_view
WHERE id IN ( SELECT /*+ CARDINALITY( tab 2 ) */ COLUMN_VALUE
FROM TABLE( NEW my_tab( 1, 2 ) ) tab );
--------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 28 | 33 (4)| 00:00:01 |
|* 1 | HASH JOIN RIGHT SEMI | | 1 | 28 | 33 (4)| 00:00:01 |
| 2 | COLLECTION ITERATOR CONSTRUCTOR FETCH| | 2 | 4 | 29 (0)| 00:00:01 |
| 3 | VIEW | MY_VIEW | 1000 | 26000 | 4 (25)| 00:00:01 |
| 4 | WINDOW SORT | | 1000 | 4000 | 4 (25)| 00:00:01 |
| 5 | TABLE ACCESS FULL | TEST | 1000 | 4000 | 3 (0)| 00:00:01 |
--------------------------------------------------------------------------------------------------
编辑:
使用内联 View 和
JOIN而不是IN使用类似的计划:SELECT /*+ CARDINALITY( tab, 2 ) */ *
FROM ( SELECT id, COUNT(1) OVER ( PARTITION BY id ) AS cnt FROM test ) t
JOIN TABLE( NEW my_tab( 1, 2 ) ) tab ON ( tab.COLUMN_VALUE = t.id );
-----------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2 | 56 | 33 (4)| 00:00:01 |
|* 1 | HASH JOIN | | 2 | 56 | 33 (4)| 00:00:01 |
| 2 | COLLECTION ITERATOR CONSTRUCTOR FETCH| | 2 | 4 | 29 (0)| 00:00:01 |
| 3 | VIEW | | 1000 | 26000 | 4 (25)| 00:00:01 |
| 4 | WINDOW SORT | | 1000 | 4000 | 4 (25)| 00:00:01 |
| 5 | TABLE ACCESS FULL | TEST | 1000 | 4000 | 3 (0)| 00:00:01 |
-----------------------------------------------------------------------------------------------
用
LEFT JOIN将GROUP BY替换为解析函数无济于事:SELECT *
FROM ( SELECT t.id, s.cnt
FROM test t
LEFT JOIN ( SELECT id, COUNT(*) AS cnt
FROM test
GROUP BY id
) s ON ( s.id = t.id )
)
WHERE id IN ( SELECT /*+ CARDINALITY( tab 2 ) */ COLUMN_VALUE
FROM TABLE( NEW my_tab( 1, 2 ) ) tab );
-----------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2 | 64 | 34 (6)| 00:00:01 |
|* 1 | HASH JOIN OUTER | | 2 | 64 | 34 (6)| 00:00:01 |
| 2 | NESTED LOOPS | | 2 | 12 | 30 (4)| 00:00:01 |
| 3 | SORT UNIQUE | | 2 | 4 | 29 (0)| 00:00:01 |
| 4 | COLLECTION ITERATOR CONSTRUCTOR FETCH| | 2 | 4 | 29 (0)| 00:00:01 |
|* 5 | INDEX UNIQUE SCAN | IDX_TEST | 1 | 4 | 0 (0)| 00:00:01 |
| 6 | VIEW | | 1000 | 26000 | 4 (25)| 00:00:01 |
| 7 | HASH GROUP BY | | 1000 | 4000 | 4 (25)| 00:00:01 |
| 8 | TABLE ACCESS FULL | TEST | 1000 | 4000 | 3 (0)| 00:00:01 |
-----------------------------------------------------------------------------------------------------
用子选择替换PL/SQL集合似乎也无济于事。考虑了CARDINALITY提示(该计划说2行)，但是索引仍然被忽略。
SELECT *
FROM ( SELECT id, cnt FROM my_view )
WHERE id IN ( SELECT /*+ CARDINALITY( tab 2 ) */ id FROM test tab );
---------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2 | 60 | 4 (25)| 00:00:01 |
| 1 | NESTED LOOPS | | 2 | 60 | 4 (25)| 00:00:01 |
| 2 | VIEW | MY_VIEW | 1000 | 26000 | 4 (25)| 00:00:01 |
| 3 | WINDOW SORT | | 1000 | 4000 | 4 (25)| 00:00:01 |
| 4 | TABLE ACCESS FULL| TEST | 1000 | 4000 | 3 (0)| 00:00:01 |
|* 5 | INDEX UNIQUE SCAN | IDX_TEST | 1 | 4 | 0 (0)| 00:00:01 |
---------------------------------------------------------------------------------
在列表中的子查询中添加
WHERE tab.id <= 2会使用索引，因此当从具有分析功能(或另一个子选择)的 View 中进行选择并按值列表进行过滤时，优化器似乎“没有足够认真地考虑CARDINALITY提示”。如何使这些查询按预期使用索引？
最佳答案
我认为一个问题可能是当the outer query block contains PL/SQL functions(例如TABLE())时，优化器拒绝合并 View (并考虑基础表上的任何索引)。
如果您手动展开 View 并直接查询表，则可以很好地访问索引:
SELECT id, COUNT(1) OVER ( PARTITION BY id ) AS cnt
FROM test
WHERE id IN ( SELECT COLUMN_VALUE
FROM TABLE( NEW my_tab( 1, 2 ) ) tab )
;
----------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 6 | 31 (4)| 00:00:01 |
| 1 | WINDOW SORT | | 1 | 6 | 31 (4)| 00:00:01 |
|* 2 | HASH JOIN SEMI | | 1 | 6 | 30 (0)| 00:00:01 |
| 3 | INDEX FULL SCAN | IDX_TEST | 1000 | 4000 | 1 (0)| 00:00:01 |
| 4 | COLLECTION ITERATOR CONSTRUCTOR FETCH| | 8168 | 16336 | 29 (0)| 00:00:01 |
----------------------------------------------------------------------------------------------------
我不确定是否有方法可以覆盖此行为，或者它是否是优化程序中的限制。我尝试将TABLE函数移至CTE，但这似乎无济于事。
关于sql - 避免在 View 中使用子查询或分析功能进行全表扫描，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/54348748/