Oracle SQL小示例系列-表连接

约定不等于承诺〃 2023-06-27 12:39 9阅读 0赞

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Oracle SQL小示例的目的，在于直接使用对应的例子来讲解SQL语法的使用，不提供理论知识的讲解，后续会根据平时开发或者学习使用来记录在Oracle SQL小示例中，如需理论知识的讲解，可以与小编沟通后续在出对应版块来讲解或者直接百度查询理解。

此篇文章，小编主要是举例表的连接关系，不建表，以level connect by 为例获取的数据作为子表来关联。

select level as lv from dual connect by level<10;

查询的结果为：

![format_png 1][]

现在分别以level<10、level<20、level<25来举例完成连接语句。

1.  内连接

**        inner join **意思是内连接 把匹配的信息全部查出来

select \* from

(select level as lv from dual connect by level<20) a

inner join (select level as lv from dual connect by level<10) b on a.lv=b.lv;

查询结果：

![format_png 2][]

2.  左连接

**left join** 左连接 意思是包含左边表所有记录，右边所有的匹配的记录，如果没有则用空补齐

select \* from

(select level as lv from dual connect by level<20) a

left join (select level as lv from dual connect by level<10) b on a.lv=b.lv;

查询结果：

![format_png 3][]

3.  右连接

**right join** 右连接  意思是包括右边表所有记录，匹配左边表的记录，如果没有则以空补齐

select \* from

(select level as lv from dual connect by level<20) a

right join (select level as lv from dual connect by level<25) b on a.lv=b.lv;

查询结果：

![format_png 4][]

4.  全连接

**full join ** 全连接 意思是左右表所有的记录全部显示出来

select \* from

(select level as lv from dual connect by level<20) a

full join (select level as lv from dual connect by level<25) b on a.lv=b.lv;

查询结果：

![format_png 5][]

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