sql嵌套查询-按父项对结果分组

问题描述

| 我需要从单个表中返回树状结果。目前，im正在使用connect by并开始使用，以确保返回所有正确的结果。

select id,parent_id
     from myTable 
 connect by prior id = parent_id start with name = \'manager\' 
     group by id,parent_id
 order by parent_id asc

但是我希望结果以树状结构返回。因此，每次找到父行时，其子行将直接显示在其下方。然后移到下一个父对象并执行相同操作 预期成绩

  - Parent A
   - child a
   - child b 
  - Parent B
   - child c
   - child d 

实际结果

- Parent A 
- Parent B
- child a 
- child b 
- child c 
- child d

是否可以在oracle中执行此操作？我的表使用parent_id字段来标识行何时具有父级。每行还有一个排序顺序，这是应该在其父项和唯一ID下排序的顺序。 我正在使用Oracle数据库     

解决方法

您想要使用use3ѭ。您所查询的排序是按

parent_id

列进行的，该列将覆盖所有层次结构的排序。 下面的查询应执行所需的操作：

with my_hierarchy_data as (
  select 1 as id,null as parent_id,\'Manager\' as name from dual union all
  select 2 as id,1 as parent_id,\'parent 1\' as name from dual union all
  select 3 as id,\'parent 2\' as name from dual union all
  select 4 as id,2 as parent_id,\'child 1\' as name from dual union all
  select 5 as id,\'child 2\' as name from dual union all
  select 6 as id,3 as parent_id,\'child 3\' as name from dual union all
  select 7 as id,\'child 4\' as name from dual 
)
select id,parent_id,lpad(\'- \',level * 2,\' \') || name as name
from my_hierarchy_data
connect by prior id = parent_id
start with name= \'Manager\'
order siblings by parent_id asc

    ,在Oracle层次查询中可以使用一个特殊值“ 6”。它为层次结构顶层的行返回1，为其子级返回2，依此类推。您可以使用它来创建缩进，如下所示：

select lpad(\'- \',level*2,\' \') || name
     from myTable 
 connect by prior id = parent_id start with name = \'manager\' 
     group by id,parent_id