从两表连接看Oracle sql优化器的效果
select emp.*,dept.* from tb_emp03 emp,tb_dept03 dept where emp.deptno=dept.id
-- 不加hint SQL> select emp.*,dept.* from tb_emp03 emp,tb_dept03 dept where emp.deptno=dept.id ; 已用时间: 00: 00: 00.00 执行计划 ---------------------------------------------------------- Plan hash value: 2666916627 -------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1818K| 97M| 3619 (2)| 00:00:44 | |* 1 | HASH JOIN | | 1818K| 97M| 3619 (2)| 00:00:44 | | 2 | TABLE ACCESS FULL| TB_DEPT03 | 10 | 160 | 3 (0)| 00:00:01 | | 3 | TABLE ACCESS FULL| TB_EMP03 | 2000K| 76M| 3601 (1)| 00:00:44 | -------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - access("EMP"."DEPTNO"="DEPT"."ID") select /*+ leading(emp,dept) use_nl(emp) */emp.*,dept.* from tb_emp03 emp,tb_dept03 dept where emp.deptno=dept.id; SQL> select /*+ leading(emp,dept) use_nl(emp) */emp.*,dept.* from tb_emp03 emp,tb_dept03 dept where emp.deptno=dept.id; 已用时间: 00: 00: 00.00 执行计划 ---------------------------------------------------------- Plan hash value: 960397288 ---------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time | ---------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1818K| 97M| | 8558 (1)| 00:01:43 | |* 1 | HASH JOIN | | 1818K| 97M| 99M| 8558 (1)| 00:01:43 | | 2 | TABLE ACCESS FULL| TB_EMP03 | 2000K| 76M| | 3601 (1)| 00:00:44 | | 3 | TABLE ACCESS FULL| TB_DEPT03 | 10 | 160 | | 3 (0)| 00:00:01 | ---------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - access("EMP"."DEPTNO"="DEPT"."ID") select /*+ leading(dept,emp) use_nldept) */emp.*,dept.* from tb_emp03 emp,tb_dept03 dept where emp.deptno=dept.id; SQL> select /*+ leading(dept,emp) use_nldept) */emp.*,dept.* from tb_emp03 emp,tb_dept03 dept where emp.deptno=dept.id; 已用时间: 00: 00: 00.00 执行计划 ---------------------------------------------------------- Plan hash value: 2666916627 -------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1818K| 97M| 3619 (2)| 00:00:44 | |* 1 | HASH JOIN | | 1818K| 97M| 3619 (2)| 00:00:44 | | 2 | TABLE ACCESS FULL| TB_DEPT03 | 10 | 160 | 3 (0)| 00:00:01 | | 3 | TABLE ACCESS FULL| TB_EMP03 | 2000K| 76M| 3601 (1)| 00:00:44 | -------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - access("EMP"."DEPTNO"="DEPT"."ID") select /*+ ordered */emp.*,dept.* from tb_emp03 emp,tb_dept03 dept where emp.deptno=dept.id; SQL> select /*+ ordered */emp.*,dept.* from tb_emp03 emp,tb_dept03 dept where emp.deptno=dept.id; 已用时间: 00: 00: 00.00 执行计划 ---------------------------------------------------------- Plan hash value: 960397288 ---------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time | ---------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1818K| 97M| | 8558 (1)| 00:01:43 | |* 1 | HASH JOIN | | 1818K| 97M| 99M| 8558 (1)| 00:01:43 | | 2 | TABLE ACCESS FULL| TB_EMP03 | 2000K| 76M| | 3601 (1)| 00:00:44 | | 3 | TABLE ACCESS FULL| TB_DEPT03 | 10 | 160 | | 3 (0)| 00:00:01 | ---------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - access("EMP"."DEPTNO"="DEPT"."ID") select /*+ use_hash(dept,emp) */emp.*,dept.* from tb_emp03 emp,tb_dept03 dept where emp.deptno=dept.id; SQL> select /*+ use_hash(dept,emp) */emp.*,dept.* from tb_emp03 emp,tb_dept03 dept where emp.deptno=dept.id; 已用时间: 00: 00: 00.00 执行计划 ---------------------------------------------------------- Plan hash value: 2666916627 -------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1818K| 97M| 3619 (2)| 00:00:44 | |* 1 | HASH JOIN | | 1818K| 97M| 3619 (2)| 00:00:44 | | 2 | TABLE ACCESS FULL| TB_DEPT03 | 10 | 160 | 3 (0)| 00:00:01 | | 3 | TABLE ACCESS FULL| TB_EMP03 | 2000K| 76M| 3601 (1)| 00:00:44 | -------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - access("EMP"."DEPTNO"="DEPT"."ID") select /*+ use_hash(emp,dept) */emp.*,dept.* from tb_emp03 emp,tb_dept03 dept where emp.deptno=dept.id; SQL> select /*+ use_hash(emp,dept) */emp.*,dept.* from tb_emp03 emp,tb_dept03 dept where emp.deptno=dept.id; 已用时间: 00: 00: 00.00 执行计划 ---------------------------------------------------------- Plan hash value: 2666916627 -------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1818K| 97M| 3619 (2)| 00:00:44 | |* 1 | HASH JOIN | | 1818K| 97M| 3619 (2)| 00:00:44 | | 2 | TABLE ACCESS FULL| TB_DEPT03 | 10 | 160 | 3 (0)| 00:00:01 | | 3 | TABLE ACCESS FULL| TB_EMP03 | 2000K| 76M| 3601 (1)| 00:00:44 | -------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - access("EMP"."DEPTNO"="DEPT"."ID")
分类:
Oracle.hint
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