sql自关联查询上级id对应的名字

Posted 2021-03-23 向往黎明小豆子

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1，表结构：city_info

　　

 

 

 2，实体类

　　

 

 

 3，sql：

　　方法一：关联查询

　　select ci1.id,(select ci2.name from city_info ci2 where ci2.id = ci1.pId) as pName,ci1.name,ci1.title,ci1.type from city_info ci1;

　　方法二：左外连接查询

　　select ci1.id,ci2.name pName,ci1.name,ci1.title,ci1.type from city_info ci1 LEFT JOIN city_info ci2 ON ci1.pId = ci2.id;

4,查询结果