Oracle的表如何连接

2024-04-02 19:55

短信预约 -IT技能 免费直播动态提醒

这篇文章主要介绍Oracle的表如何连接，文中介绍的非常详细，具有一定的参考价值，感兴趣的小伙伴们一定要看完！

Oracle表连接方法有四种：
● 排序合并连接（Sort Merge Join）
● 嵌套循环连接（Nested Loops Join）
● 哈希连接（Hash Join）
● 笛卡尔积（Cartesian Product）

如果where条件有exists、in或=any操作符+子查询，则Oracle会将其处理为半连接，执行计划中对应的关键字为SEMI。

SQL> select department_id,department_name from departments d where exists (select 1 from employees e where d.department_id = e.department_id and e.salary > 2500);

11 rows selected.

Execution Plan
----------------------------------------------------------
Plan hash value: 2188966913

--------------------------------------------------------------------------------------------
| Id | Operation                    | Name        | Rows | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |             |    10 |   230 |     6 (17)| 00:00:01 |
|   1 | MERGE JOIN SEMI             |             |    10 |   230 |     6 (17)| 00:00:01 |
|   2 |   TABLE ACCESS BY INDEX ROWID| DEPARTMENTS |    27 |   432 |     2   (0)| 00:00:01 |
|   3 |    INDEX FULL SCAN           | DEPT_ID_PK |    27 |       |     1   (0)| 00:00:01 |
|* 4 |   SORT UNIQUE                |             |   105 |   735 |     4 (25)| 00:00:01 |
|* 5 |    TABLE ACCESS FULL         | EMPLOYEES   |   105 |   735 |     3   (0)| 00:00:01 |
--------------------------------------------------------------------------------------------

SQL> select department_id,department_name from departments d where department_id in (select department_id from employees e where d.department_id = e.department_id and e.salary > 2500);

11 rows selected.

Execution Plan
----------------------------------------------------------
Plan hash value: 2188966913

SQL> select department_id,department_name from departments d where department_id=any(select department_id from employees e where d.department_id = e.department_id and e.salary > 2500);

11 rows selected.

Execution Plan
----------------------------------------------------------
Plan hash value: 2188966913

以上是“Oracle的表如何连接”这篇文章的所有内容，感谢各位的阅读！希望分享的内容对大家有帮助，更多相关知识，欢迎关注亿速云行业资讯频道！

免责声明：

① 本站未注明“稿件来源”的信息均来自网络整理。其文字、图片和音视频稿件的所属权归原作者所有。本站收集整理出于非商业性的教育和科研之目的，并不意味着本站赞同其观点或证实其内容的真实性。仅作为临时的测试数据，供内部测试之用。本站并未授权任何人以任何方式主动获取本站任何信息。

② 本站未注明“稿件来源”的临时测试数据将在测试完成后最终做删除处理。有问题或投稿请发送至: 邮箱/279061341@qq.com QQ/279061341

阅读原文内容投诉