ORACLE中的索引与组合索引比对
同一张表上的两个字段，都比较经常查询，用组合索引好呢？还是分开索引好呢？
看下面一个例子：
create table TB1
(
OWNER VARCHAR2(30) not null,
OBJECT_NAME VARCHAR2(30) not null,
SUBOBJECT_NAME VARCHAR2(30),
OBJECT_ID NUMBER not null,
DATA_OBJECT_ID NUMBER,
OBJECT_TYPE VARCHAR2(19),
CREATED DATE not null,
LAST_DDL_TIME DATE not null,
TIMESTAMP VARCHAR2(19),
STATUS VARCHAR2(7),
TEMPORARY VARCHAR2(1),
GENERATED VARCHAR2(1),
SECONDARY VARCHAR2(1)
)
===========================
列数 object_type
1 20020 SYNONYM
2 16359 JAVA CLASS
先在表上建组合索引INX_TB1_OTYPE_ONAME;
SQL> select * from tb1 where object_type='SYNONYM';
已选择20020行。
执行计划
----------------------------------------------------------
Plan hash value: 3226679318
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1720 | 146K| 149 (3)| 00:00:02 |
|* 1 | TABLE ACCESS FULL| TB1 | 1720 | 146K| 149 (3)| 00:00:02 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("OBJECT_TYPE"='SYNONYM')
统计信息
----------------------------------------------------------
1 recursive calls
0 db block gets
1957 consistent gets
0 physical reads
0 redo size
942680 bytes sent via SQL*Net to client
15059 bytes received via SQL*Net from client
1336 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
20020 rows processed
可以发现不走索引，全表扫描。
SQL> select * from tb1 where object_type='SYNONYM' and object_name='DEPT';
未选定行
执行计划
----------------------------------------------------------
Plan hash value: 480521530
--------------------------------------------------------------------------------
-------------------
| Id | Operation | Name | Rows | Bytes | Cost
(%CPU)| Time |
--------------------------------------------------------------------------------
-------------------
| 0 | SELECT STATEMENT | | 1 | 87 |
2 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| TB1 | 1 | 87 |
2 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | INX_TB1_OTYPE_ONAME | 1 | |
1 (0)| 00:00:01 |
--------------------------------------------------------------------------------
-------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("OBJECT_TYPE"='SYNONYM' AND "OBJECT_NAME"='DEPT')
统计信息
----------------------------------------------------------
1 recursive calls
0 db block gets
2 consistent gets
0 physical reads
0 redo size
992 bytes sent via SQL*Net to client
374 bytes received via SQL*Net from client
1 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
0 rows processed
走索引了。
分别两个字段建索引
SQL> select * from tb1 where object_type='SYNONYM';
已选择20020行。
执行计划
----------------------------------------------------------
Plan hash value: 419929180
--------------------------------------------------------------------------------
-------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU
)| Time |
--------------------------------------------------------------------------------
-------------
| 0 | SELECT STATEMENT | | 1720 | 146K| 64 (0
)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| TB1 | 1720 | 146K| 64 (0
)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | INX_TB1_OTYPE | 1720 | | 5 (0
)| 00:00:01 |
--------------------------------------------------------------------------------
-------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("OBJECT_TYPE"='SYNONYM')
统计信息
----------------------------------------------------------
1 recursive calls
0 db block gets
3240 consistent gets
0 physical reads
0 redo size
2184300 bytes sent via SQL*Net to client
15059 bytes received via SQL*Net from client
1336 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
20020 rows processed
单走索引，但逻辑读很高。
SQL> select * from tb1 where object_type='SYNONYM' and object_name='DEPT';
未选定行
执行计划
----------------------------------------------------------
Plan hash value: 447681844
-------------------------------------------------------------------------------
-------------
| Id | Operation | Name | Rows | Bytes | Cost (%CP
)| Time |
-------------------------------------------------------------------------------
-------------
| 0 | SELECT STATEMENT | | 1 | 87 | 2 (
)| 00:00:01 |
|* 1 | TABLE ACCESS BY INDEX ROWID| TB1 | 1 | 87 | 2 (
)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | INX_TB1_ONAME | 2 | | 1 (
)| 00:00:01 |
-------------------------------------------------------------------------------
-------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("OBJECT_TYPE"='SYNONYM')
2 - access("OBJECT_NAME"='DEPT')
统计信息
----------------------------------------------------------
1 recursive calls
0 db block gets
3 consistent gets
0 physical reads
0 redo size
992 bytes sent via SQL*Net to client
374 bytes received via SQL*Net from client
1 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
0 rows processed
走INX_TB1_ONAME 索引 逻辑读略高
SQL> select /*+NO_INDEX(tb1 INX_TB1_OTYPE)*/* from tb1 where object_type='SYNONY
M';
已选择20020行。
执行计划
----------------------------------------------------------
Plan hash value: 3226679318
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1720 | 146K| 149 (3)| 00:00:02 |
|* 1 | TABLE ACCESS FULL| TB1 | 1720 | 146K| 149 (3)| 00:00:02 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("OBJECT_TYPE"='SYNONYM')
统计信息
----------------------------------------------------------
1 recursive calls
0 db block gets
1957 consistent gets
0 physical reads
0 redo size
942680 bytes sent via SQL*Net to client
15059 bytes received via SQL*Net from client
1336 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
20020 rows processed
不走索引，效率更高。
看下面一个例子：
create table TB1
(
OWNER VARCHAR2(30) not null,
OBJECT_NAME VARCHAR2(30) not null,
SUBOBJECT_NAME VARCHAR2(30),
OBJECT_ID NUMBER not null,
DATA_OBJECT_ID NUMBER,
OBJECT_TYPE VARCHAR2(19),
CREATED DATE not null,
LAST_DDL_TIME DATE not null,
TIMESTAMP VARCHAR2(19),
STATUS VARCHAR2(7),
TEMPORARY VARCHAR2(1),
GENERATED VARCHAR2(1),
SECONDARY VARCHAR2(1)
)
===========================
列数 object_type
1 20020 SYNONYM
2 16359 JAVA CLASS
先在表上建组合索引INX_TB1_OTYPE_ONAME;
SQL> select * from tb1 where object_type='SYNONYM';
已选择20020行。
执行计划
----------------------------------------------------------
Plan hash value: 3226679318
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1720 | 146K| 149 (3)| 00:00:02 |
|* 1 | TABLE ACCESS FULL| TB1 | 1720 | 146K| 149 (3)| 00:00:02 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("OBJECT_TYPE"='SYNONYM')
统计信息
----------------------------------------------------------
1 recursive calls
0 db block gets
1957 consistent gets
0 physical reads
0 redo size
942680 bytes sent via SQL*Net to client
15059 bytes received via SQL*Net from client
1336 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
20020 rows processed
可以发现不走索引，全表扫描。
SQL> select * from tb1 where object_type='SYNONYM' and object_name='DEPT';
未选定行
执行计划
----------------------------------------------------------
Plan hash value: 480521530
--------------------------------------------------------------------------------
-------------------
| Id | Operation | Name | Rows | Bytes | Cost
(%CPU)| Time |
--------------------------------------------------------------------------------
-------------------
| 0 | SELECT STATEMENT | | 1 | 87 |
2 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| TB1 | 1 | 87 |
2 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | INX_TB1_OTYPE_ONAME | 1 | |
1 (0)| 00:00:01 |
--------------------------------------------------------------------------------
-------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("OBJECT_TYPE"='SYNONYM' AND "OBJECT_NAME"='DEPT')
统计信息
----------------------------------------------------------
1 recursive calls
0 db block gets
2 consistent gets
0 physical reads
0 redo size
992 bytes sent via SQL*Net to client
374 bytes received via SQL*Net from client
1 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
0 rows processed
走索引了。
分别两个字段建索引
SQL> select * from tb1 where object_type='SYNONYM';
已选择20020行。
执行计划
----------------------------------------------------------
Plan hash value: 419929180
--------------------------------------------------------------------------------
-------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU
)| Time |
--------------------------------------------------------------------------------
-------------
| 0 | SELECT STATEMENT | | 1720 | 146K| 64 (0
)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| TB1 | 1720 | 146K| 64 (0
)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | INX_TB1_OTYPE | 1720 | | 5 (0
)| 00:00:01 |
--------------------------------------------------------------------------------
-------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("OBJECT_TYPE"='SYNONYM')
统计信息
----------------------------------------------------------
1 recursive calls
0 db block gets
3240 consistent gets
0 physical reads
0 redo size
2184300 bytes sent via SQL*Net to client
15059 bytes received via SQL*Net from client
1336 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
20020 rows processed
单走索引，但逻辑读很高。
SQL> select * from tb1 where object_type='SYNONYM' and object_name='DEPT';
未选定行
执行计划
----------------------------------------------------------
Plan hash value: 447681844
-------------------------------------------------------------------------------
-------------
| Id | Operation | Name | Rows | Bytes | Cost (%CP
)| Time |
-------------------------------------------------------------------------------
-------------
| 0 | SELECT STATEMENT | | 1 | 87 | 2 (
)| 00:00:01 |
|* 1 | TABLE ACCESS BY INDEX ROWID| TB1 | 1 | 87 | 2 (
)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | INX_TB1_ONAME | 2 | | 1 (
)| 00:00:01 |
-------------------------------------------------------------------------------
-------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("OBJECT_TYPE"='SYNONYM')
2 - access("OBJECT_NAME"='DEPT')
统计信息
----------------------------------------------------------
1 recursive calls
0 db block gets
3 consistent gets
0 physical reads
0 redo size
992 bytes sent via SQL*Net to client
374 bytes received via SQL*Net from client
1 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
0 rows processed
走INX_TB1_ONAME 索引 逻辑读略高
SQL> select /*+NO_INDEX(tb1 INX_TB1_OTYPE)*/* from tb1 where object_type='SYNONY
M';
已选择20020行。
执行计划
----------------------------------------------------------
Plan hash value: 3226679318
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1720 | 146K| 149 (3)| 00:00:02 |
|* 1 | TABLE ACCESS FULL| TB1 | 1720 | 146K| 149 (3)| 00:00:02 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("OBJECT_TYPE"='SYNONYM')
统计信息
----------------------------------------------------------
1 recursive calls
0 db block gets
1957 consistent gets
0 physical reads
0 redo size
942680 bytes sent via SQL*Net to client
15059 bytes received via SQL*Net from client
1336 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
20020 rows processed
不走索引，效率更高。