Oracle SQL join on都有什么方式表达?
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我们经常使用 join相关语句做关联查询,那么在join连接方式后边,on 结合and 和 where结果会发生什么变化呢?
在使用 join on 时 注意 and where 区别和如何使用
join on and
join on and 方式 类似于 on 条件1 and on 条件2,都是 基于join 关联两个表结果 ,取出关联后数据。 举例如下
select t2.object_id t2_id from t1 right join t2 on t1.object_id=t2.object_id and t1.object_id=1989;
--输出结果太多,省略,看 下边access部分
92937 rows selected.
Elapsed: 00:00:05.33
Execution Plan
Plan hash value: 2539735012
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 102K| 2609K| 372 (1)| 00:00:05 |
|* 1 | HASH JOIN RIGHT OUTER| | 102K| 2609K| 372 (1)| 00:00:05 |
|* 2 | INDEX RANGE SCAN | T1_IDX | 1 | 13 | 1 (0)| 00:00:01 |
| 3 | TABLE ACCESS FULL | T2 | 102K| 1304K| 371 (1)| 00:00:05 |
Predicate Information (identified by operation id):
1 - access("T1"."OBJECT_ID"(+)="T2"."OBJECT_ID") -- t1 右连接 t2的 object_id,以t2输出为主,也就是输出t2所有内容
2 - access("T1"."OBJECT_ID"(+)=1989) --同上,输出1989所有页游内容(这个条件在此可以忽略)
Note
- dynamic sampling used for this statement (level=2)
Statistics
16 recursive calls
0 db block gets
7580 consistent gets
1 physical reads
0 redo size
1699670 bytes sent via SQL*Net to client
68668 bytes received via SQL*Net from client
6197 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
92937 rows processed1
join on where
join on where ,是 join on连接之后对结果再进行筛选(为达到执行效率最有,是先进性where条件筛选,再join关联),举例如下
SQL> select t2.object_id t2_id from t1 www.sangpi.comright join t2 on t1.object_id=t2.object_id where t1.object_id=1989;
T2_ID
1989
Elapsed: 00:00:00.06
Execution Plan
Plan hash value: 2511910206
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 1 | 26 | 2 (0)| 00:00:01 |
| 1 | MERGE JOIN CARTESIAN| | 1 | 26 | 2 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | T2_IDX | 1 | 13 | 1 (0)| 00:00:01 |
| 3 | BUFFER SORT | | 1 | 13 | 1 (0)| 00:00:01 |
|* 4 | INDEX RANGE SCAN | T1_IDX | 1 | 13 | 1 (0)| 00:00:01 |
Predicate Information (identified by operation id):
2 - access("T2"."OBJECT_ID"=1989)
4 - access("T1"."OBJECT_ID"=1989)
Note
- dynamic sampling used for this statement (level=2)
Statistics
21 recursive calls
0 db block gets
147 consistent gets
3 physical reads
0 redo size
524 bytes sent via SQL*Net to client
523 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
1 rows processed
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