这里给一个常识性的，SQL中like与索引使用的原则。很熟悉的朋友可以飘过鸟~~
1.包含一百万行记录的测试表
sec@ora10g> select count(*) from t;
COUNT(*)
----------
1000000
2.在x列上创建索引
sec@ora10g> create index i_t on t(x);
Index created.
3.直接查询，可以利用到索引
sec@ora10g> set autot trace exp
sec@ora10g> select * from t where x = 'SEC';
Execution Plan
----------------------------------------------------------
Plan hash value: 2928007915
------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1214 | 101K| 51 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| T | 1214 | 101K| 51 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | I_T | 1214 | | 5 (0)| 00:00:01 |
------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("X"='SEC')
4.以like 'SEC%'形式进行查询，可以利用到索引
sec@ora10g> select * from t where x like 'SEC%';
Execution Plan
----------------------------------------------------------
Plan hash value: 2928007915
------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1214 | 101K| 51 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| T | 1214 | 101K| 51 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | I_T | 1214 | | 5 (0)| 00:00:01 |
------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("X" LIKE 'SEC%')
filter("X" LIKE 'SEC%')
5.以not like 'SEC%'形式进行查询，无法利用到索引
sec@ora10g> select * from t where x not like 'SEC%';
Execution Plan
----------------------------------------------------------
Plan hash value: 1601196873
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1000K| 82M| 2840 (2)| 00:00:35 |
|* 1 | TABLE ACCESS FULL| T | 1000K| 82M| 2840 (2)| 00:00:35 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("X" NOT LIKE 'SEC%')
6.以like '%SEC'形式进行查询，无法利用到索引
sec@ora10g> select * from t where x like '%SEC';
Execution Plan
----------------------------------------------------------
Plan hash value: 1601196873
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 50103 | 4207K| 2826 (1)| 00:00:34 |
|* 1 | TABLE ACCESS FULL| T | 50103 | 4207K| 2826 (1)| 00:00:34 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("X" LIKE '%SEC')
7.同样道理，以like '%SEC%'形式进行查询，同样也无法利用到索引
sec@ora10g> select * from t where x like '%SEC%';
Execution Plan
----------------------------------------------------------
Plan hash value: 1601196873
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 50103 | 4207K| 2826 (1)| 00:00:34 |
|* 1 | TABLE ACCESS FULL| T | 50103 | 4207K| 2826 (1)| 00:00:34 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("X" LIKE '%SEC%')
8.小结
LIKE '%***'、LIKE '%***%'及NOT LIKE语句无法使用到索引；
尽量不使用LIKE语句，不可避免时，可使用like ' ***%'。
-- The End --
1.包含一百万行记录的测试表
sec@ora10g> select count(*) from t;
COUNT(*)
----------
1000000
2.在x列上创建索引
sec@ora10g> create index i_t on t(x);
Index created.
3.直接查询，可以利用到索引
sec@ora10g> set autot trace exp
sec@ora10g> select * from t where x = 'SEC';
Execution Plan
----------------------------------------------------------
Plan hash value: 2928007915
------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1214 | 101K| 51 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| T | 1214 | 101K| 51 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | I_T | 1214 | | 5 (0)| 00:00:01 |
------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("X"='SEC')
4.以like 'SEC%'形式进行查询，可以利用到索引
sec@ora10g> select * from t where x like 'SEC%';
Execution Plan
----------------------------------------------------------
Plan hash value: 2928007915
------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1214 | 101K| 51 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| T | 1214 | 101K| 51 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | I_T | 1214 | | 5 (0)| 00:00:01 |
------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("X" LIKE 'SEC%')
filter("X" LIKE 'SEC%')
5.以not like 'SEC%'形式进行查询，无法利用到索引
sec@ora10g> select * from t where x not like 'SEC%';
Execution Plan
----------------------------------------------------------
Plan hash value: 1601196873
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1000K| 82M| 2840 (2)| 00:00:35 |
|* 1 | TABLE ACCESS FULL| T | 1000K| 82M| 2840 (2)| 00:00:35 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("X" NOT LIKE 'SEC%')
6.以like '%SEC'形式进行查询，无法利用到索引
sec@ora10g> select * from t where x like '%SEC';
Execution Plan
----------------------------------------------------------
Plan hash value: 1601196873
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 50103 | 4207K| 2826 (1)| 00:00:34 |
|* 1 | TABLE ACCESS FULL| T | 50103 | 4207K| 2826 (1)| 00:00:34 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("X" LIKE '%SEC')
7.同样道理，以like '%SEC%'形式进行查询，同样也无法利用到索引
sec@ora10g> select * from t where x like '%SEC%';
Execution Plan
----------------------------------------------------------
Plan hash value: 1601196873
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 50103 | 4207K| 2826 (1)| 00:00:34 |
|* 1 | TABLE ACCESS FULL| T | 50103 | 4207K| 2826 (1)| 00:00:34 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("X" LIKE '%SEC%')
8.小结
LIKE '%***'、LIKE '%***%'及NOT LIKE语句无法使用到索引；
尽量不使用LIKE语句，不可避免时，可使用like ' ***%'。
-- The End --
来自 “ ITPUB博客 ” ，链接：https://blog.itpub.net/70034820/viewspace-2994002/ ，如需转载，请注明出处，否则将追究法律责任。
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