与B树索引相关的执行计划

来源:互联网 时间:1970-01-01

索引唯一扫描,索引范围扫描,索引全扫描,索引快速全扫描和索引跳跃式扫描。索引唯一扫描: 

SQL> create table employee(gender varchar2(1),employee_id number);Table created.SQL> insert into employee values('F',99);1 row created.SQL> insert into employee values('F',100);1 row created.SQL> insert into employee values('M',101);1 row created. SQL> insert into employee values('M',102);1 row created.SQL> insert into employee values('M',103);1 row created.SQL> insert into employee values('M',104);1 row created.SQL> insert into employee values('M',105);1 row created.SQL> insert into employee values('F',106);1 row created.SQL> commit;Commit complete.SQL> create unique index idx_unqi_emp on employee(employee_id);Index created.SQL> select * from employee where employee_id=100;G EMPLOYEE_ID- -----------F 100SQL> set lines 200 pagesize 1000SQL> select plan_table_output from table(dbms_xplan.display_cursor(null,null,'ALL'));PLAN_TABLE_OUTPUT---------------------------------------------------------------------------------SQL_IDbum8qv24s6tqp, child number 0-------------------------------------select * from employee where employee_id=100Plan hash value: 1037614268--------------------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |--------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | | | 1 (100)| || 1 | TABLE ACCESS BY INDEX ROWID| EMPLOYEE | 1 |15 | 1 (0)| 00:00:01 ||* 2 | INDEX UNIQUE SCAN | IDX_UNQI_EMP | 1 | | 0 (0)| |---------------------------------------------------------------------------------31 rows selected.

 


 
索引范围扫描:
 
SQL> drop index idx_unqi_emp;Index dropped.SQL> create index idx_unqi_emp on employee(employee_id);Index created.SQL> select * from employee where employee_id=100;G EMPLOYEE_ID- -----------F 100SQL> select plan_table_output from table(dbms_xplan.display_cursor(null,null,'ALL'));PLAN_TABLE_OUTPUT-----------------------------------------------------------------------------------------------------------------------------------------SQL_IDbum8qv24s6tqp, child number 0select * from employee where employee_id=100Plan hash value: 407794244--------------------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |--------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | | | 2 (100)| || 1 | TABLE ACCESS BY INDEX ROWID| EMPLOYEE | 1 |15 | 2 (0)| 00:00:01 ||* 2 | INDEX RANGE SCAN | IDX_UNQI_EMP | 1 | | 1 (0)| 00:00:01 |--------------------------------------------------------------------------------------------

 


索引快速全扫描:
 
SQL> begin 2 for i in 1..5000 loop 3 insert into employee values('F',i); 4 end loop; 5 commit; 6 end; 7 /PL/SQL procedure successfully completed.SQL> begin 2 for i in 5001..10000 loop 3 insert into employee values('M',i); 4 end loop; 5 commit; 6 end; 7 /PL/SQL procedure successfully completed.SQL> select gender,count(*) from employee group by gender;G COUNT(*)- ----------M5000F5000BEGIN DBMS_STATS.GATHER_TABLE_STATS(ownname => 'SCOTT', tabname => 'EMPLOYEE', estimate_percent => 100, method_opt => 'for all columns size repeat', no_invalidate => FALSE, degree => 8, granularity => 'ALL', cascade => TRUE); END;PL/SQL procedure successfully completed.SQL> set autot traceSQL> select employee_id from employee;10000 rows selected.Execution Plan----------------------------------------------------------Plan hash value: 2119105728------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 10000 | 40000 | 7 (0)| 00:00:01 || 1 | TABLE ACCESS FULL| EMPLOYEE | 10000 | 40000 | 7 (0)| 00:00:01 |------------------------------------------------------------------------------

 


 
提示走索引,无效,因为employee_id有null值:
 
SQL> create index idx_emp_1 on employee(employee_id);Index created.SQL> select /*+ index(employee idx_emp_1) */ employee_id from employee;10000 rows selected.Execution Plan----------------------------------------------------------Plan hash value: 2119105728------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 10000 | 40000 | 7 (0)| 00:00:01 || 1 | TABLE ACCESS FULL| EMPLOYEE | 10000 | 40000 | 7 (0)| 00:00:01 |------------------------------------------------------------------------------

 


建立组合索引,或许把employee_id限制为非空:
 
SQL> select /*+ index(employee idx_emp_1) */ employee_id from employee;10000 rows selected.Execution Plan----------------------------------------------------------Plan hash value: 438557521------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 10000 | 40000 | 25 (0)| 00:00:01 || 1 | INDEX FULL SCAN | IDX_EMP_1 | 10000 | 40000 | 25 (0)| 00:00:01 |------------------------------------------------------------------------------

 


 
索引跳跃扫描:
SQL> create index idx_emp_1 on employee(gender,employee_id);Index created.SQL> select * from employee where employee_id=109;Execution Plan----------------------------------------------------------Plan hash value: 2039022311------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1 | 6 | 3 (0)| 00:00:01 ||* 1 | INDEX SKIP SCAN | IDX_EMP_1 | 1 | 6 | 3 (0)| 00:00:01 |------------------------------------------------------------------------------Predicate Information (identified by operation id):--------------------------------------------------- 1 - access("EMPLOYEE_ID"=109) filter("EMPLOYEE_ID"=109)Statistics---------------------------------------------------------- 1 recursive calls 0 db block gets 6 consistent gets 3 physical reads 0 redo size 600 bytes sent via SQL*Net to client 524 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed

 





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