java 关于获取数据库中父子级关系的数据

通过 super.变量名 获取父类中的变量值

举例：

public class Parent{//定义父类Parent public int a=1//定义父类中的一个变量a}public class Son extend Parent{//定义子类son，继承父类parent public void show(){ int b = super.a//通过super访问父类变量a，获取值赋值给b }}

select t1.name,t2.name,t3.name,t4.name

from tb as t1

left join tb as t2 on t2.pid=t1.id and t2.pid=1

left join tb as t3 on t3.pid=t2.id and t3.pid=2

left join tb as t4 on t4.pid=t3.id and t4.pid=3

where pid=0

加多一列层级码，会简单很多比如亚洲用‘01’ 中国用‘0101’，北京用‘010101‘，海定用‘01010101’，东城用’01010102‘

这样语句可以

select id as col1,(select name from 表 where code = SubString(a.Code, 1,2)) as col2,

(select name from 表 where code = SubString(a.Code, 3,2)) as col3,

(select name from 表 where code = SubString(a.Code, 5,2)) as col4,

(select name from 表 where code = SubString(a.Code, 7,2)) as col5

from 表 a where Type = 'Distric'

不然

(select d.name from 表 b, 表 c, 表 d where a.parentid = b.id and b.parentid = c.id

and c.parentid = d.id) as col2,...

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