sql

Question

我有以下层次结构：

A -> E -> C -> D
|
|
|-> B -> D

这是闭包 table 我想出了：

| Ancestor | Descendant | Depth |
|    A     |     A      |   0   |
|    B     |     B      |   0   | 
|    C     |     C      |   0   | 
|    D     |     D      |   0   | 
|    E     |     E      |   0   | 
|    A     |     E      |   1   | 
|    A     |     B      |   1   | 
|    A     |     C      |   2   | 
|    E     |     C      |   1   | 
|    A     |     D      |   3   | 
|    E     |     D      |   2   | 
|    C     |     D      |   1   | 
|    A     |     D      |   2   | 
|    B     |     D      |   1   |

我想删除 B 和 D 之间的 link，因此我想删除 A 和 [=17] 之间的 link =]（深度之一2）。问题是我不想删除深度 3 的 A 和 D 之间的 link，因为我没有删除 link 之间的 C 和 D.

目前，这里是 SQL 语句，用于列出我要删除的 link：

SELECT link.ancestor, link.descendant, link.depth
FROM closure_table p,
     closure_table link,
     closure_table c
WHERE p.ancestor = link.ancestor
  AND c.descendant = link.descendant
  AND p.descendant = B
  AND c.ancestor = D;

但是这条语句给了我不想删除的行：

| Ancestor | Descendant | Depth |
|    A     |     D      |   2   |
|    A     |     D      |   3   |  <- As said before, I want to keep this one
|    B     |     D      |   1   |

Answer 1

您可以select具有所有相同祖先-后代对的最小深度的祖先-后代对：

with edges(s, e) as (
   -- the pairs to be removed
   select 'A', 'D'
   union all
   select 'B', 'D'
),
n_l as (
   select c.* from closure c where c.ancestor != c.descendant
)
select c.* from n_l c where exists (select 1 from edges e where e.s = c.ancestor and e.e = c.descendant) 
and c.depth = (select min(c1.depth) from n_l c1 where c1.ancestor = c.ancestor and c1.descendant = c.descendant);

输出：

ancestor	descendant	depth
A	D	2
B	D	1

Answer 2

我想我找到了解决方案，对于那些感兴趣的人：

declare @Descendant nchar(10) = 'D';
declare @Ancestor nchar(10) = 'B';

with cte as
(
  select Ancestor, Depth
  from closure_table
  where Descendant = @Descendant
  and Ancestor = @Ancestor
  and Depth = 1
union all
  select r.Ancestor, l.Depth + 1 as Depth
  from cte as l
  join closure_table as r on r.Descendant = l.Ancestor
  where r.Depth = 1
)
delete closure_table
from closure_table
join cte on cte.Ancestor = closure_table.Ancestor and cte.Depth = closure_table.Depth
where closure_table.Descendant = @Descendant;

sql - 在具有多个相同路径的闭包 table 中删除

sql - Deletion in closure table with multiple same paths

postgresql

transitive-closure-table