原 Oracle视图中含有rownum导致不能走索引

2024年4月22日  

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Tags： Oracle原创索引rownum

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目录

• 现象
• 模拟
• 总结
• 参考

现象

环境：oracle 11.2.0.4

今天客户说，一个视图查询很慢，让帮忙分析。

分析后，发现是rownum导致的视图不能走索引。

模拟

对原查询进行简化模拟：

这里modify_time列为varchar2类型，但是因为某些原因，web应用查询该字段必须使用date类型，所以我在该列上创建了函数索引：

DROP TABLE TB; CREATE TABLE TB(ID INT, modify_time varchar2(14)); INSERT INTO TB (id,modify_time) SELECT rownum, to_char(sysdate + rownum,'YYYYMMDDHH24MISS') from dual CONNECT BY LEVEL <= 20000; create index idx_1 on tb(to_date(modify_time,'YYYYMMDDHH24MISS')); create index idx_2 on tb(modify_time); begin DBMS_STATS.gather_table_stats('lhr', 'tb',cascade => TRUE, DEGREE=>16,no_invalidate => false); end; create or replace view vw1 as select id,modify_time,to_date(modify_time,'YYYYMMDDHH24MISS') modify_at,to_date(modify_time,'YYYYMMDDHH24miss') modify_at1 from tb ; create or replace view vw2 as select id,modify_time,to_date(modify_time,'YYYYMMDDHH24MISS') modify_at,rownum rn from tb ; -- 走索引 select * from vw1 where modify_time= '2024-03-01'; select * from vw1 where modify_at= to_date('2024-03-01','yyyy-mm-dd'); select * from vw1 where modify_at= to_date('20240301000000','syyyy-mm-dd hh24:mi:ss'); -- 不走索引（to_date函数大小写问题） select * from vw1 where modify_at1= to_date('2024-03-01','yyyy-mm-dd'); -- 不走索引（rownum问题） select * from vw2 where modify_at= to_date('2024-03-01','yyyy-mm-dd'); select * from vw2 where modify_time= '2024-03-01';

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DROP TABLE TB; CREATE TABLE TB(ID INT, modify_time varchar2(14));   INSERT INTO TB (id,modify_time) SELECT rownum, to_char(sysdate +  rownum,'YYYYMMDDHH24MISS') from dual CONNECT BY LEVEL <= 20000;   create index idx_1 on tb(to_date(modify_time,'YYYYMMDDHH24MISS')); create index idx_2 on tb(modify_time);   begin DBMS_STATS.gather_table_stats('lhr', 'tb',cascade => TRUE, DEGREE=>16,no_invalidate => false); end;   create or replace view vw1 as select id,modify_time,to_date(modify_time,'YYYYMMDDHH24MISS') modify_at,to_date(modify_time,'YYYYMMDDHH24miss') modify_at1   from  tb ;   create or replace view vw2 as select id,modify_time,to_date(modify_time,'YYYYMMDDHH24MISS') modify_at,rownum rn   from  tb ;   -- 走索引   select * from vw1  where  modify_time= '2024-03-01'; select * from vw1  where  modify_at= to_date('2024-03-01','yyyy-mm-dd'); select * from vw1  where  modify_at= to_date('20240301000000','syyyy-mm-dd hh24:mi:ss');   -- 不走索引（to_date函数大小写问题） select * from vw1  where  modify_at1= to_date('2024-03-01','yyyy-mm-dd');   -- 不走索引（rownum问题） select * from vw2  where  modify_at= to_date('2024-03-01','yyyy-mm-dd'); select * from vw2  where  modify_time= '2024-03-01';

执行计划：

SYS@LHR11G> conn lhr/lhr Connected. LHR@LHR11G> set autot on LHR@LHR11G> select * from vw1 where modify_at= to_date('2024-03-01','yyyy-mm-dd'); no rows selected Execution Plan ---------------------------------------------------------- Plan hash value: 4159717772 ------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 31 | 1 (0)| 00:00:01 | | 1 | TABLE ACCESS BY INDEX ROWID| TB | 1 | 31 | 1 (0)| 00:00:01 | |* 2 | INDEX RANGE SCAN | IDX_1 | 1 | | 1 (0)| 00:00:01 | ------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - access(TO_DATE("MODIFY_TIME",'YYYYMMDDHH24MISS')=TO_DATE(' 2024-03-01 00:00:00', 'syyyy-mm-dd hh24:mi:ss')) Note ----- - dynamic sampling used for this statement (level=2) Statistics ---------------------------------------------------------- 21 recursive calls 0 db block gets 150 consistent gets 1 physical reads 0 redo size 473 bytes sent via SQL*Net to client 512 bytes received via SQL*Net from client 1 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 0 rows processed LHR@LHR11G> select * from vw1 where modify_at= to_date('20240301000000','syyyy-mm-dd hh24:mi:ss'); no rows selected Execution Plan ---------------------------------------------------------- Plan hash value: 4159717772 ------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 31 | 1 (0)| 00:00:01 | | 1 | TABLE ACCESS BY INDEX ROWID| TB | 1 | 31 | 1 (0)| 00:00:01 | |* 2 | INDEX RANGE SCAN | IDX_1 | 1 | | 1 (0)| 00:00:01 | ------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - access(TO_DATE("MODIFY_TIME",'YYYYMMDDHH24MISS')=TO_DATE('202403010000 00','syyyy-mm-dd hh24:mi:ss')) Note ----- - dynamic sampling used for this statement (level=2) Statistics ---------------------------------------------------------- 21 recursive calls 0 db block gets 150 consistent gets 0 physical reads 0 redo size 473 bytes sent via SQL*Net to client 512 bytes received via SQL*Net from client 1 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 0 rows processed LHR@LHR11G> select * from vw1 where modify_at1= to_date('2024-03-01','yyyy-mm-dd'); no rows selected Execution Plan ---------------------------------------------------------- Plan hash value: 2878482057 -------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 31 | 22 (0)| 00:00:01 | |* 1 | TABLE ACCESS FULL| TB | 1 | 31 | 22 (0)| 00:00:01 | -------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter(TO_DATE("MODIFY_TIME",'YYYYMMDDHH24miss')=TO_DATE(' 2024-03-01 00:00:00', 'syyyy-mm-dd hh24:mi:ss')) Note ----- - dynamic sampling used for this statement (level=2) Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 76 consistent gets 0 physical reads 0 redo size 473 bytes sent via SQL*Net to client 512 bytes received via SQL*Net from client 1 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 0 rows processed LHR@LHR11G> select * from vw2 where modify_at= to_date('2024-03-01','yyyy-mm-dd'); no rows selected Execution Plan ---------------------------------------------------------- Plan hash value: 1470101981 ---------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ---------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 19745 | 674K| 22 (0)| 00:00:01 | |* 1 | VIEW | VW2 | 19745 | 674K| 22 (0)| 00:00:01 | | 2 | COUNT | | | | | | | 3 | TABLE ACCESS FULL| TB | 19745 | 424K| 22 (0)| 00:00:01 | ---------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter("MODIFY_AT"=TO_DATE(' 2024-03-01 00:00:00', 'syyyy-mm-dd hh24:mi:ss')) Note ----- - dynamic sampling used for this statement (level=2) Statistics ---------------------------------------------------------- 21 recursive calls 0 db block gets 216 consistent gets 0 physical reads 0 redo size 465 bytes sent via SQL*Net to client 512 bytes received via SQL*Net from client 1 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 0 rows processed LHR@LHR11G> select * from vw1 where modify_time= '2024-03-01'; no rows selected Execution Plan ---------------------------------------------------------- Plan hash value: 956939525 ------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 31 | 1 (0)| 00:00:01 | | 1 | TABLE ACCESS BY INDEX ROWID| TB | 1 | 31 | 1 (0)| 00:00:01 | |* 2 | INDEX RANGE SCAN | IDX_2 | 1 | | 1 (0)| 00:00:01 | ------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - access("MODIFY_TIME"='2024-03-01') Note ----- - dynamic sampling used for this statement (level=2) Statistics ---------------------------------------------------------- 37 recursive calls 0 db block gets 81 consistent gets 0 physical reads 0 redo size 546 bytes sent via SQL*Net to client 512 bytes received via SQL*Net from client 1 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 0 rows processed LHR@LHR11G> select * from vw2 where modify_time= '2024-03-01'; no rows selected Execution Plan ---------------------------------------------------------- Plan hash value: 1470101981 ---------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ---------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 19745 | 848K| 22 (0)| 00:00:01 | |* 1 | VIEW | VW2 | 19745 | 848K| 22 (0)| 00:00:01 | | 2 | COUNT | | | | | | | 3 | TABLE ACCESS FULL| TB | 19745 | 597K| 22 (0)| 00:00:01 | ---------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter("MODIFY_TIME"='2024-03-01') Note ----- - dynamic sampling used for this statement (level=2) Statistics ---------------------------------------------------------- 21 recursive calls 0 db block gets 218 consistent gets 0 physical reads 0 redo size 538 bytes sent via SQL*Net to client 512 bytes received via SQL*Net from client 1 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 0 rows processed LHR@LHR11G>

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SYS@LHR11G> conn lhr/lhr Connected. LHR@LHR11G> set autot on LHR@LHR11G> select * from vw1  where  modify_at= to_date('2024-03-01','yyyy-mm-dd');   no rows selected   Execution Plan ---------------------------------------------------------- Plan hash value: 4159717772   ------------------------------------------------------------------------------------- | Id  | Operation                   | Name  | Rows  | Bytes | Cost (%CPU)| Time     | ------------------------------------------------------------------------------------- |   0 | SELECT STATEMENT            |       |     1 |    31 |     1   (0)| 00:00:01 | |   1 |  TABLE ACCESS BY INDEX ROWID| TB    |     1 |    31 |     1   (0)| 00:00:01 | |*  2 |   INDEX RANGE SCAN          | IDX_1 |     1 |       |     1   (0)| 00:00:01 | -------------------------------------------------------------------------------------   Predicate Information (identified by operation id): ---------------------------------------------------      2 - access(TO_DATE("MODIFY_TIME",'YYYYMMDDHH24MISS')=TO_DATE(' 2024-03-01               00:00:00', 'syyyy-mm-dd hh24:mi:ss'))   Note -----    - dynamic sampling used for this statement (level=2)   Statistics ----------------------------------------------------------          21  recursive calls           0  db block gets         150  consistent gets           1  physical reads           0  redo size         473  bytes sent via SQL*Net to client         512  bytes received via SQL*Net from client           1  SQL*Net roundtrips to/from client           0  sorts (memory)           0  sorts (disk)           0  rows processed   LHR@LHR11G> select * from vw1  where  modify_at= to_date('20240301000000','syyyy-mm-dd hh24:mi:ss');   no rows selected   Execution Plan ---------------------------------------------------------- Plan hash value: 4159717772   ------------------------------------------------------------------------------------- | Id  | Operation                   | Name  | Rows  | Bytes | Cost (%CPU)| Time     | ------------------------------------------------------------------------------------- |   0 | SELECT STATEMENT            |       |     1 |    31 |     1   (0)| 00:00:01 | |   1 |  TABLE ACCESS BY INDEX ROWID| TB    |     1 |    31 |     1   (0)| 00:00:01 | |*  2 |   INDEX RANGE SCAN          | IDX_1 |     1 |       |     1   (0)| 00:00:01 | -------------------------------------------------------------------------------------   Predicate Information (identified by operation id): ---------------------------------------------------      2 - access(TO_DATE("MODIFY_TIME",'YYYYMMDDHH24MISS')=TO_DATE('202403010000               00','syyyy-mm-dd hh24:mi:ss'))   Note -----    - dynamic sampling used for this statement (level=2)   Statistics ----------------------------------------------------------          21  recursive calls           0  db block gets         150  consistent gets           0  physical reads           0  redo size         473  bytes sent via SQL*Net to client         512  bytes received via SQL*Net from client           1  SQL*Net roundtrips to/from client           0  sorts (memory)           0  sorts (disk)           0  rows processed   LHR@LHR11G> select * from vw1  where  modify_at1= to_date('2024-03-01','yyyy-mm-dd');   no rows selected   Execution Plan ---------------------------------------------------------- Plan hash value: 2878482057   -------------------------------------------------------------------------- | Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     | -------------------------------------------------------------------------- |   0 | SELECT STATEMENT  |      |     1 |    31 |    22   (0)| 00:00:01 | |*  1 |  TABLE ACCESS FULL| TB   |     1 |    31 |    22   (0)| 00:00:01 | --------------------------------------------------------------------------   Predicate Information (identified by operation id): ---------------------------------------------------      1 - filter(TO_DATE("MODIFY_TIME",'YYYYMMDDHH24miss')=TO_DATE('               2024-03-01 00:00:00', 'syyyy-mm-dd hh24:mi:ss'))   Note -----    - dynamic sampling used for this statement (level=2)   Statistics ----------------------------------------------------------           0  recursive calls           0  db block gets          76  consistent gets           0  physical reads           0  redo size         473  bytes sent via SQL*Net to client         512  bytes received via SQL*Net from client           1  SQL*Net roundtrips to/from client           0  sorts (memory)           0  sorts (disk)           0  rows processed   LHR@LHR11G> select * from vw2  where  modify_at= to_date('2024-03-01','yyyy-mm-dd');   no rows selected   Execution Plan ---------------------------------------------------------- Plan hash value: 1470101981   ---------------------------------------------------------------------------- | Id  | Operation           | Name | Rows  | Bytes | Cost (%CPU)| Time     | ---------------------------------------------------------------------------- |   0 | SELECT STATEMENT    |      | 19745 |   674K|    22   (0)| 00:00:01 | |*  1 |  VIEW               | VW2  | 19745 |   674K|    22   (0)| 00:00:01 | |   2 |   COUNT             |      |       |       |            |          | |   3 |    TABLE ACCESS FULL| TB   | 19745 |   424K|    22   (0)| 00:00:01 | ----------------------------------------------------------------------------   Predicate Information (identified by operation id): ---------------------------------------------------      1 - filter("MODIFY_AT"=TO_DATE(' 2024-03-01 00:00:00', 'syyyy-mm-dd               hh24:mi:ss'))   Note -----    - dynamic sampling used for this statement (level=2)   Statistics ----------------------------------------------------------          21  recursive calls           0  db block gets         216  consistent gets           0  physical reads           0  redo size         465  bytes sent via SQL*Net to client         512  bytes received via SQL*Net from client           1  SQL*Net roundtrips to/from client           0  sorts (memory)           0  sorts (disk)           0  rows processed   LHR@LHR11G> select * from vw1  where  modify_time= '2024-03-01';   no rows selected   Execution Plan ---------------------------------------------------------- Plan hash value: 956939525   ------------------------------------------------------------------------------------- | Id  | Operation                   | Name  | Rows  | Bytes | Cost (%CPU)| Time     | ------------------------------------------------------------------------------------- |   0 | SELECT STATEMENT            |       |     1 |    31 |     1   (0)| 00:00:01 | |   1 |  TABLE ACCESS BY INDEX ROWID| TB    |     1 |    31 |     1   (0)| 00:00:01 | |*  2 |   INDEX RANGE SCAN          | IDX_2 |     1 |       |     1   (0)| 00:00:01 | -------------------------------------------------------------------------------------   Predicate Information (identified by operation id): ---------------------------------------------------      2 - access("MODIFY_TIME"='2024-03-01')   Note -----    - dynamic sampling used for this statement (level=2)   Statistics ----------------------------------------------------------          37  recursive calls           0  db block gets          81  consistent gets           0  physical reads           0  redo size         546  bytes sent via SQL*Net to client         512  bytes received via SQL*Net from client           1  SQL*Net roundtrips to/from client           0  sorts (memory)           0  sorts (disk)           0  rows processed   LHR@LHR11G> select * from vw2  where  modify_time= '2024-03-01';   no rows selected   Execution Plan ---------------------------------------------------------- Plan hash value: 1470101981   ---------------------------------------------------------------------------- | Id  | Operation           | Name | Rows  | Bytes | Cost (%CPU)| Time     | ---------------------------------------------------------------------------- |   0 | SELECT STATEMENT    |      | 19745 |   848K|    22   (0)| 00:00:01 | |*  1 |  VIEW               | VW2  | 19745 |   848K|    22   (0)| 00:00:01 | |   2 |   COUNT             |      |       |       |            |          | |   3 |    TABLE ACCESS FULL| TB   | 19745 |   597K|    22   (0)| 00:00:01 | ----------------------------------------------------------------------------   Predicate Information (identified by operation id): ---------------------------------------------------      1 - filter("MODIFY_TIME"='2024-03-01')   Note -----    - dynamic sampling used for this statement (level=2)   Statistics ----------------------------------------------------------          21  recursive calls           0  db block gets         218  consistent gets           0  physical reads           0  redo size         538  bytes sent via SQL*Net to client         512  bytes received via SQL*Net from client           1  SQL*Net roundtrips to/from client           0  sorts (memory)           0  sorts (disk)           0  rows processed   LHR@LHR11G>

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