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oracle 交集,并集,差集

2013-08-20 00:38 295 查看
create table test1
(
name varchar(10),
NN varchar(10)
);
insert into test1 values('test','A');
insert into test1 values('test1','B');
insert into test1 values('test1','C');
insert into test1 values('test1','D');
insert into test1 values('test1','E');
create table test2
(
name varchar(10),
NN varchar(10)
);
insert into test2 values('test','A');
insert into test2 values('test2','B');
insert into test2 values('test2','C');
insert into test2 values('test2','D');
insert into test2 values('test2','E');


1、交集:intersect

SQL> select * from test1 intersect select * from test2;

NAME       NN
---------- ----------
test       A


2、并集:union、union all (注意两者的区别)

SQL> select * from test1 union select * from test2;

NAME       NN
---------- ----------
test       A
test1      B
test1      C
test1      D
test1      E
test2      B
test2      C
test2      D
test2      E

9 rows selected.


SQL> select * from test1 union all select * from test2;

NAME       NN
---------- ----------
test       A
test1      B
test1      C
test1      D
test1      E
test       A
test2      B
test2      C
test2      D
test2      E

10 rows selected.


3、差集:minus

SQL> select * from test1 minus select * from test2;

NAME       NN
---------- ----------
test1      B
test1      C
test1      D
test1      E

SQL> select * from test2 minus select * from test1;

NAME       NN
---------- ----------
test2      B
test2      C
test2      D
test2      E


最后对于求交集用intersect效率高呢还是hash join效率高呢?

SQL> select * from test1 intersect select * from test2;

Execution Plan
----------------------------------------------------------
Plan hash value: 4290880088

-----------------------------------------------------------------------------
| Id  | Operation           | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |       |     5 |   140 |     8  (63)| 00:00:01 |
|   1 |  INTERSECTION       |       |       |       |            |          |
|   2 |   SORT UNIQUE       |       |     5 |    70 |     4  (25)| 00:00:01 |
|   3 |    TABLE ACCESS FULL| TEST1 |     5 |    70 |     3   (0)| 00:00:01 |
|   4 |   SORT UNIQUE       |       |     5 |    70 |     4  (25)| 00:00:01 |
|   5 |    TABLE ACCESS FULL| TEST2 |     5 |    70 |     3   (0)| 00:00:01 |
-----------------------------------------------------------------------------

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

Statistics
----------------------------------------------------------
0  recursive calls
0  db block gets
14  consistent gets
0  physical reads
0  redo size
590  bytes sent via SQL*Net to client
523  bytes received via SQL*Net from client
2  SQL*Net roundtrips to/from client
2  sorts (memory)
0  sorts (disk)
1  rows processed

SQL> select a.* from test1 a,test2 b where a.name=b.name and a.nn=b.nn;

Execution Plan
----------------------------------------------------------
Plan hash value: 497311279

----------------------------------------------------------------------------
| Id  | Operation          | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |       |     5 |   140 |     7  (15)| 00:00:01 |
|*  1 |  HASH JOIN         |       |     5 |   140 |     7  (15)| 00:00:01 |
|   2 |   TABLE ACCESS FULL| TEST1 |     5 |    70 |     3   (0)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| TEST2 |     5 |    70 |     3   (0)| 00:00:01 |
----------------------------------------------------------------------------

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

1 - access("A"."NAME"="B"."NAME" AND "A"."NN"="B"."NN")

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

Statistics
----------------------------------------------------------
0  recursive calls
0  db block gets
15  consistent gets
0  physical reads
0  redo size
590  bytes sent via SQL*Net to client
523  bytes received via SQL*Net from client
2  SQL*Net roundtrips to/from client
0  sorts (memory)
0  sorts (disk)
1  rows processed


cost值intersect比hash join 高,但是逻辑读intersect比hash join的低。不知道大量数据的时候,会是什么样
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