sql嵌套查询-按父级分组结果

Question

我需要从单个表中返回树状结果。目前我使用 connect by 和 start with 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。然后移动到下一个父母并做同样的事情

预期结果

  - 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

在 oracle 中可以做到这一点吗？我的表使用 parent_id 字段来识别行何时有父级。每行也有一个排序顺序，这是它应该在其父级下排序的顺序和一个唯一的 Id。

我正在使用 Oracle 数据库

Answer 1

你想要的是使用ORDER SIBLINGS BY。您的查询按parent_id 列排序，该列覆盖任何层次排序。

下面的查询应该做你需要做的事情：

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, 1 as parent_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, 2 as parent_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, 3 as parent_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

Answer 2

有一个特殊值level 可用于Oracle 分层查询。它为层次结构顶层的行返回 1，为其子行返回 2，依此类推。您可以使用它来创建这样的缩进：

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