hint no_expand
lnnvl在执行计划中,这是函数
1,no_expand对于where条件中出现in列表或出现or的查询,不会考虑or扩展
2,一般情况下,优化器会使用or扩展,假如不使用or扩展代价更低,会使用or扩展

SQL> explain plan for select emp.* from emp,dept where emp.mgr=3 or dept.deptno=
30;

已解释。

SQL> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

Plan hash value: 613092161

--------------------------------------------------------------------------------

-

--------------------------------------------------------------------------------

-

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 15 | 630 | 5 (0)| 00:00:01
|

| 1 | CONCATENATION | | | | |
|

| 2 | NESTED LOOPS | | 12 | 504 | 2 (0)| 00:00:01
|

|* 3 | INDEX UNIQUE SCAN | PK_DEPT | 1 | 3 | 0 (0)| 00:00:01
|

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

| 4 | TABLE ACCESS FULL | EMP | 12 | 468 | 2 (0)| 00:00:01
|

| 5 | MERGE JOIN CARTESIAN| | 3 | 126 | 3 (0)| 00:00:01
|

|* 6 | TABLE ACCESS FULL | EMP | 1 | 39 | 2 (0)| 00:00:01
|

| 7 | BUFFER SORT | | 7 | 21 | 1 (0)| 00:00:01

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

|

|* 8 | INDEX FULL SCAN | PK_DEPT | 7 | 21 | 1 (0)| 00:00:01
|

--------------------------------------------------------------------------------

-

Predicate Information (identified by operation id):
---------------------------------------------------

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

   3 - access("DEPT"."DEPTNO"=30)
   6 - filter("EMP"."MGR"=3)
   8 - filter(LNNVL("DEPT"."DEPTNO"=30))

已选择22行。

SQL> explain plan for select /*+ no_expand() */ emp.* from emp,dept where emp.mg
r=3 or dept.deptno=30;

已解释。

SQL> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

Plan hash value: 3941739098

--------------------------------------------------------------------------------

-

--------------------------------------------------------------------------------

-

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 15 | 630 | 6 (0)| 00:00:01
|

| 1 | NESTED LOOPS | | 15 | 630 | 6 (0)| 00:00:01
|

| 2 | TABLE ACCESS FULL | EMP | 12 | 468 | 2 (0)| 00:00:01
|

|* 3 | INDEX FAST FULL SCAN| PK_DEPT | 1 | 3 | 0 (0)| 00:00:01
|

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

-

Predicate Information (identified by operation id):
---------------------------------------------------

3 - filter("EMP"."MGR"=3 OR "DEPT"."DEPTNO"=30)

已选择15行。

no_fact
1,用于星形转换中,此提示指示查询表不能用于事实表

ITPub博客

oracle hint_no_expand_no_fact

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