表的三大连接的使用限制

三大连接的使用限制

1 hash Join的连接限制
hash join 不支持连接条件是大于、小于、不等于和like的场景. 因为hash join是一种经典的等值算法。

语句1 ：连接条件为大于，结果无法根据hint走hash join

set linesize 1000
set autotrace traceonly explain
select /*+ leading(t1) use_hash(t2)*/ * from t1,t2 where t1.id>t2.t1_id and t1.n=9;
ZBB@test>select /*+ leading(t1) use_hash(t2)*/ * from t1,t2 where t1.id>t2.t1_id and t1.n=9;

Execution Plan
----------------------------------------------------------
Plan hash value: 1967407726

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |  5591 |    21M|   276   (1)| 00:00:01 |
|   1 |  NESTED LOOPS      |      |  5591 |    21M|   276   (1)| 00:00:01 |
|*  2 |   TABLE ACCESS FULL| T1   |     1 |  2028 |     3   (0)| 00:00:01 |
|*  3 |   TABLE ACCESS FULL| T2   |  5591 |    10M|   273   (1)| 00:00:01 |
---------------------------------------------------------------------------

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

   2 - filter("T1"."N"=9)
   3 - filter("T1"."ID">"T2"."T1_ID")

Note
-----
   - dynamic sampling used for this statement (level=2)

语句2 ，当连接条件为小于时，结果无法根据hint走hash join

select /*+ leading(t1) use_hash(t2)*/ * from t1,t2 where t1.id<t2.t1_id and t1.n=9;
ZBB@test>select /*+ leading(t1) use_hash(t2)*/ * from t1,t2 where t1.id<t2.t1_id and t1.n=9;

Execution Plan
----------------------------------------------------------
Plan hash value: 1967407726

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |  5591 |    21M|   276   (1)| 00:00:01 |
|   1 |  NESTED LOOPS      |      |  5591 |    21M|   276   (1)| 00:00:01 |
|*  2 |   TABLE ACCESS FULL| T1   |     1 |  2028 |     3   (0)| 00:00:01 |
|*  3 |   TABLE ACCESS FULL| T2   |  5591 |    10M|   273   (1)| 00:00:01 |
---------------------------------------------------------------------------

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

   2 - filter("T1"."N"=9)
   3 - filter("T1"."ID"<"T2"."T1_ID")

Note
-----
   - dynamic sampling used for this statement (level=2)

语句3 ，当连接条件为不等于的时候，无法根据hint走hash join

select /*+ leading(t1) use_hash(t2)*/ * from t1,t2 where t1.id<>t2.t1_id and t1.n=9;  
ZBB@test>select /*+ leading(t1) use_hash(t2)*/ * from t1,t2 where t1.id<>t2.t1_id and t1.n=9;

Execution Plan
----------------------------------------------------------
Plan hash value: 1967407726

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |   111K|   433M|   276   (1)| 00:00:01 |
|   1 |  NESTED LOOPS      |      |   111K|   433M|   276   (1)| 00:00:01 |
|*  2 |   TABLE ACCESS FULL| T1   |     1 |  2028 |     3   (0)| 00:00:01 |
|*  3 |   TABLE ACCESS FULL| T2   |   111K|   217M|   273   (1)| 00:00:01 |
---------------------------------------------------------------------------

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

   2 - filter("T1"."N"=9)
   3 - filter("T1"."ID"<>"T2"."T1_ID")

Note
-----
   - dynamic sampling used for this statement (level=2)

ZBB@test>

语句4，当连接条件为like的时候，无法根据hint走hash join

select /*+ leading(t1) use_hash(t2)*/ * from t1,t2 where t1.id like t2.t1_id and t1.n=9; --
ZBB@test>select /*+ leading(t1) use_hash(t2)*/ * from t1,t2 where t1.id like t2.                                                                             t1_id and t1.n=9;

Execution Plan
----------------------------------------------------------
Plan hash value: 1967407726

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |  5591 |    21M|   276   (1)| 00:00:01 |
|   1 |  NESTED LOOPS      |      |  5591 |    21M|   276   (1)| 00:00:01 |
|*  2 |   TABLE ACCESS FULL| T1   |     1 |  2028 |     3   (0)| 00:00:01 |
|*  3 |   TABLE ACCESS FULL| T2   |  5591 |    10M|   273   (1)| 00:00:01 |
---------------------------------------------------------------------------

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

   2 - filter("T1"."N"=9)
   3 - filter(TO_CHAR("T1"."ID") LIKE TO_CHAR("T2"."T1_ID"))

Note
-----
   - dynamic sampling used for this statement (level=2)

ZBB@test>

2 排序合并连接的限制
merge sort join 支持连接条件是大于、小于的场景，但是不支持不等于和like的场景。

语句1 当条件为大于的时候，merge sort join支持这个算法，可以根据hint走merge sort join

set autotrace traceonly explain
select /*+ leading(t1) use_merge(t2)*/ * from t1,t2 where t1.id>t2.t1_id and t1.n=9;
ZBB@test>select /*+ leading(t1) use_merge(t2)*/ * from t1,t2 where t1.id>t2.t1_id and t1.n=9;

Execution Plan
----------------------------------------------------------
Plan hash value: 412793182

------------------------------------------------------------------------------------
| Id  | Operation           | Name | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |      |  5591 |    21M|       | 47920   (1)| 00:00:11 |
|   1 |  MERGE JOIN         |      |  5591 |    21M|       | 47920   (1)| 00:00:11 |
|   2 |   SORT JOIN         |      |     1 |  2028 |       |     4  (25)| 00:00:01 |
|*  3 |    TABLE ACCESS FULL| T1   |     1 |  2028 |       |     3   (0)| 00:00:01 |
|*  4 |   SORT JOIN         |      |   111K|   217M|   582M| 47916   (1)| 00:00:11 |
|   5 |    TABLE ACCESS FULL| T2   |   111K|   217M|       |   273   (1)| 00:00:01 |
------------------------------------------------------------------------------------

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

   3 - filter("T1"."N"=9)
   4 - access(INTERNAL_FUNCTION("T1"."ID")>INTERNAL_FUNCTION("T2"."T1_ID"))
       filter(INTERNAL_FUNCTION("T1"."ID")>INTERNAL_FUNCTION("T2"."T1_ID"))

Note
-----
   - dynamic sampling used for this statement (level=2)

语句2 ，条件为小于

select /*+ leading(t1) use_merge(t2)*/ * from t1,t2 where t1.id<t2.t1_id and t1.n=9;
ZBB@test>select /*+ leading(t1) use_merge(t2)*/ * from t1,t2 where t1.id<t2.t1_id and t1.n=9;

Execution Plan
----------------------------------------------------------
Plan hash value: 412793182

------------------------------------------------------------------------------------
| Id  | Operation           | Name | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |      | 99949 |    11M|       |  1849   (1)| 00:00:01 |
|   1 |  MERGE JOIN         |      | 99949 |    11M|       |  1849   (1)| 00:00:01 |
|   2 |   SORT JOIN         |      |     1 |    57 |       |     4  (25)| 00:00:01 |
|*  3 |    TABLE ACCESS FULL| T1   |     1 |    57 |       |     3   (0)| 00:00:01 |
|*  4 |   SORT JOIN         |      | 99999 |  6445K|    15M|  1845   (1)| 00:00:01 |
|   5 |    TABLE ACCESS FULL| T2   | 99999 |  6445K|       |   273   (1)| 00:00:01 |
------------------------------------------------------------------------------------

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

   3 - filter("T1"."N"=9)
   4 - access("T1"."ID"<"T2"."T1_ID")
       filter("T1"."ID"<"T2"."T1_ID")

语句3 当条件为不等于

select /*+ leading(t1) use_merge(t2)*/ * from t1,t2 where t1.id<>t2.t1_id and t1.n=9;
ZBB@test>select /*+ leading(t1) use_merge(t2)*/ * from t1,t2 where t1.id<>t2.t1_id and t1.n=9;

Execution Plan
----------------------------------------------------------
Plan hash value: 1967407726

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      | 99998 |    11M|   276   (1)| 00:00:01 |
|   1 |  NESTED LOOPS      |      | 99998 |    11M|   276   (1)| 00:00:01 |
|*  2 |   TABLE ACCESS FULL| T1   |     1 |    57 |     3   (0)| 00:00:01 |
|*  3 |   TABLE ACCESS FULL| T2   | 99998 |  6445K|   273   (1)| 00:00:01 |
---------------------------------------------------------------------------

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

   2 - filter("T1"."N"=9)
   3 - filter("T1"."ID"<>"T2"."T1_ID")

ZBB@test>

语句4 当条件为like

select /*+ leading(t1) use_merge(t2)*/ * from t1,t2 where t1.id like t2.t1_id and t1.n=9;
ZBB@test>select /*+ leading(t1) use_merge(t2)*/ * from t1,t2 where t1.id like t2.t1_id and t1.n=9;

Execution Plan
----------------------------------------------------------
Plan hash value: 1967407726

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |  5000 |   600K|   276   (1)| 00:00:01 |
|   1 |  NESTED LOOPS      |      |  5000 |   600K|   276   (1)| 00:00:01 |
|*  2 |   TABLE ACCESS FULL| T1   |     1 |    57 |     3   (0)| 00:00:01 |
|*  3 |   TABLE ACCESS FULL| T2   |  5000 |   322K|   273   (1)| 00:00:01 |
---------------------------------------------------------------------------

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

   2 - filter("T1"."N"=9)
   3 - filter(TO_CHAR("T1"."ID") LIKE TO_CHAR("T2"."T1_ID"))

ZBB@test>

3 nested Loop 的连接限制

从上面的例子可以看到。当hint提示不起作用的时候，走的就是nested loop. 所以，nested loop join是没有任何限制的。

END

表的三大连接的使用限制

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