left join 可以不加ON
时间: 2023-10-15 12:07:26 浏览: 69
LEFT JOIN 可以不加ON,但是这样做会得到一个笛卡尔积(Cartesian product)的结果。在没有ON子句的情况下,LEFT JOIN 会返回左表中的每一行与右表中的每一行的组合。这种组合会导致结果集的行数急剧增加,并且可能会给查询结果带来很大的混乱。因此,一般情况下,在使用 LEFT JOIN 时,都会加上一个 ON 子句来指定连接条件,从而得到更准确和有意义的结果。引用<span class="em">1</span><span class="em">2</span><span class="em">3</span>
#### 引用[.reference_title]
- *1* [sql中的left join及on、where条件关键字的区别详解](https://download.csdn.net/download/weixin_38722184/12824978)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v93^chatsearchT3_2"}}] [.reference_item style="max-width: 33.333333333333336%"]
- *2* [sql left join on 条件不写可以吗 会怎么样](https://blog.csdn.net/damei2017/article/details/87971363)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v93^chatsearchT3_2"}}] [.reference_item style="max-width: 33.333333333333336%"]
- *3* [LEFT JOIN的时候应该用ON还是WHERE](https://blog.csdn.net/lyb8010/article/details/112389651)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v93^chatsearchT3_2"}}] [.reference_item style="max-width: 33.333333333333336%"]
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