left join 3张表关联

anli

表A---------------------------------关联第一张表B-----------------------关联第二张表c

select * fomr 表名A　　left join 表B  on  表A字段=表B的id 　　left join 表c 　on 表A字段=表c的id　　　

案例：

 SELECT 
    sheng.NAME AS  省,
    sheng.CODE AS 省编号, 	
    shi.NAME AS 市,
    shi.CODE AS 市编号, 
	xian.NAME AS 县,
    xian.CODE AS 县编号 
    FROM  area as sheng  
  
      LEFT JOIN area shi 
      ON    shi.perent_code = sheng.code   
	  LEFT JOIN area xian 
	  on   xian.perent_code = shi.code  
	  where
	  
	  xian.code='371721';
	  //  sheng.name='山东省';

+--------+--------+--------+--------+------+--------+
| 省     | 省编号 | 市     | 市编号 | 县   | 县编号 |
+--------+--------+--------+--------+------+--------+
| 山东省 | 370000 | 菏泽市 | 371700 | 曹县 | 371721 |
+--------+--------+--------+--------+------+--------+