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【YashanDB知识库】filter or改写问题

news 来源：原创 2024/9/19 8:53:55

问题现象

当filter中出现or的时候，会导致filter无法走索引或者走hash join，就需要进行改写，例如：

create table test_tab1(col1 int, col2 int, col3 int);
create table test_tab2(col4 int, col5 int, col6 int);begin
for i in 1..10000 loopinsert into test_tab1 values (i,i+1,i+2);insert into test_tab2 values (i,i+1,i+2);
endloop;
commit;
end;
/exec DBMS_STATS.GATHER_TABLE_STATS('SYS', 'test_tab1', null, 1, FALSE, 'FOR ALL COLUMNS SIZE AUTO', 4, 'AUTO', TRUE);
exec DBMS_STATS.GATHER_TABLE_STATS('SYS', 'test_tab2', null, 1, FALSE, 'FOR ALL COLUMNS SIZE AUTO', 4, 'AUTO', TRUE);select * from test_tab1, test_tab2 where col1=col4 or col2=col5;select * from test_tab1, test_tab2 where col1=col4
union all
select * from test_tab1, test_tab2 where col1<>col4 and col2=col5;create unique index idx1 on test_tab1(col1);
create unique index idx2 on test_tab1(col2);exec DBMS_STATS.GATHER_TABLE_STATS('SYS', 'test_tab1', null, 1, FALSE, 'FOR ALL COLUMNS SIZE AUTO', 4, 'AUTO', TRUE);
exec DBMS_STATS.GATHER_TABLE_STATS('SYS', 'test_tab2', null, 1, FALSE, 'FOR ALL COLUMNS SIZE AUTO', 4, 'AUTO', TRUE);select * from test_tab1 where col1=5 or col2=5;select * from test_tab1 where col1=5
union all
select * from test_tab1 where col1<>5 and col2=5;

执行计划：

SQL> explain select * from test_tab1, test_tab2 where col1=col4 or col2=col5;PLAN_DESCRIPTION
----------------------------------------------------------------
SQL hash value: 1783492608
Optimizer: ADOPT_C+----+--------------------------------+----------------------+------------+----------+-------------+--------------------------------+
| Id | Operation type | Name | Owner | Rows | Cost(%CPU) | Partition info |
+----+--------------------------------+----------------------+------------+----------+-------------+--------------------------------+
| 0 | SELECT STATEMENT | | | | | |
|* 1 | NESTED LOOPS INNER | | | 15003| 16082( 0)| |
| 2 | TABLE ACCESS FULL | TEST_TAB1 | SYS | 10000| 24( 0)| |
| 3 | TABLE ACCESS FULL | TEST_TAB2 | SYS | 10000| 24( 0)| |
+----+--------------------------------+----------------------+------------+----------+-------------+--------------------------------+Operation Information (identified by operation id):
---------------------------------------------------1 - Predicate : filter("TEST_TAB1"."COL2" = "TEST_TAB2"."COL5" OR "TEST_TAB1"."COL1" = "TEST_TAB2"."COL4")16 rows fetched.SQL> explain select * from test_tab1, test_tab2 where col1=col4
union all3 select * from test_tab1, test_tab2 where col1<>col4 and col2=col5;PLAN_DESCRIPTION
----------------------------------------------------------------
SQL hash value: 2495885085
Optimizer: ADOPT_C+----+--------------------------------+----------------------+------------+----------+-------------+--------------------------------+
| Id | Operation type | Name | Owner | Rows | Cost(%CPU) | Partition info |
+----+--------------------------------+----------------------+------------+----------+-------------+--------------------------------+
| 0 | SELECT STATEMENT | | | | | |
| 1 | VIEW | | | 20000| 111( 0)| |
| 2 | UNION ALL | | | 20000| 111( 0)| |
|* 3 | HASH JOIN INNER | | | 10000| 54( 0)| |
| 4 | TABLE ACCESS FULL | TEST_TAB1 | SYS | 10000| 24( 0)| |
| 5 | TABLE ACCESS FULL | TEST_TAB2 | SYS | 10000| 24( 0)| |
|* 6 | HASH JOIN INNER | | | 10000| 54( 0)| |
| 7 | TABLE ACCESS FULL | TEST_TAB1 | SYS | 10000| 24( 0)| |
| 8 | TABLE ACCESS FULL | TEST_TAB2 | SYS | 10000| 24( 0)| |
+----+--------------------------------+----------------------+------------+----------+-------------+--------------------------------+Operation Information (identified by operation id):
---------------------------------------------------3 - Predicate : access("TEST_TAB1"."COL1" = "TEST_TAB2"."COL4")6 - Predicate : access("TEST_TAB1"."COL2" = "TEST_TAB2"."COL5")filter("TEST_TAB1"."COL1" <> "TEST_TAB2"."COL4")23 rows fetched.SQL> explain select * from test_tab1 where col1=5 or col2=5;PLAN_DESCRIPTION
----------------------------------------------------------------
SQL hash value: 3573759094
Optimizer: ADOPT_C+----+--------------------------------+----------------------+------------+----------+-------------+--------------------------------+
| Id | Operation type | Name | Owner | Rows | Cost(%CPU) | Partition info |
+----+--------------------------------+----------------------+------------+----------+-------------+--------------------------------+
| 0 | SELECT STATEMENT | | | | | |
|* 1 | TABLE ACCESS FULL | TEST_TAB1 | SYS | 2| 25( 0)| |
+----+--------------------------------+----------------------+------------+----------+-------------+--------------------------------+Operation Information (identified by operation id):
---------------------------------------------------1 - Predicate : filter("TEST_TAB1"."COL1" = 5 OR "TEST_TAB1"."COL2" = 5)14 rows fetched.SQL> explain select * from test_tab1 where col1=5
union all3 select * from test_tab1 where col1<>5 and col2=5;PLAN_DESCRIPTION
----------------------------------------------------------------
SQL hash value: 2073754267
Optimizer: ADOPT_C+----+--------------------------------+----------------------+------------+----------+-------------+--------------------------------+
| Id | Operation type | Name | Owner | Rows | Cost(%CPU) | Partition info |
+----+--------------------------------+----------------------+------------+----------+-------------+--------------------------------+
| 0 | SELECT STATEMENT | | | | | |
| 1 | VIEW | | | 2| 1( 0)| |
| 2 | UNION ALL | | | 2| 1( 0)| |
| 3 | TABLE ACCESS BY INDEX ROWID | TEST_TAB1 | SYS | 1| 1( 0)| |
|* 4 | INDEX UNIQUE SCAN | IDX1 | SYS | 1| 1( 0)| |
|* 5 | TABLE ACCESS BY INDEX ROWID | TEST_TAB1 | SYS | 1| 1( 0)| |
|* 6 | INDEX UNIQUE SCAN | IDX2 | SYS | 1| 1( 0)| |
+----+--------------------------------+----------------------+------------+----------+-------------+--------------------------------+Operation Information (identified by operation id):
---------------------------------------------------4 - Predicate : access("TEST_TAB1"."COL1" = 5)5 - Predicate : filter("TEST_TAB1"."COL1" <> 5)6 - Predicate : access("TEST_TAB1"."COL2" = 5)21 rows fetched.

执行时间：

SQL> select * from test_tab1, test_tab2 where col1=col4 or col2=col5;...10000 rows fetched.Elapsed: 00:00:45.263SQL> select * from test_tab1, test_tab2 where col1=col4
union all3 select * from test_tab1, test_tab2 where col1<>col4 and col2=col5;...10000 rows fetched.Elapsed: 00:00:00.447SQL> select * from test_tab1 where col1=5 or col2=5;COL1 COL2 COL3
------------ ------------ ------------4 5 65 6 72 rows fetched.Elapsed: 00:00:00.004SQL> select * from test_tab1 where col1=5
union all2 3 select * from test_tab1 where col1<>5 and col2=5;COL1 COL2 COL3
------------ ------------ ------------5 6 74 5 62 rows fetched.Elapsed: 00:00:00.000