postgres 层次结构 - child 级别的计数并按 children 或 grandchildren 的日期排序

Question

我想知道如何编写 postgres 子查询，以便下面的 table 示例能够输出我需要的内容。

id   parent_id    postdate

1    　　-1      2015-03-10 
2 　　　　1      2015-03-11  (child level 1)
3　　　　 1      2015-03-12  (child level 1)
4　　　　 3      2015-03-13  (child level 2)
5　　　　-1      2015-03-14
6　　　　-1      2015-03-15
7　　　　 6      2015-03-16  (child level 1)

如果我想按 child 级别 1 对所有根 ID 进行排序，parent 的计数为 children(s)，输出将是这样的

id    count　     date
6　　　2　　　  2015-03-15
1　　　4　　　  2015-03-10
5　　　1　　　  2015-03-14

输出根据根的 child 按发布日期排序。输出的 'date' 是根的发布日期。尽管 id#5 的发布日期较新，但 rootid#6 的 child (id#7) 具有最新的发布日期，因为它是按 child 的发布日期排序的。 id#5 没有任何 children 所以它只是放在最后，按日期排序。 'count' 是数字 children（child 级别 1），grandchildren（child 级别 2）和它本身（根）。例如，id #2、#3、#4 都属于 id#1，所以对于 id#1，计数将为 4。

到目前为止我当前的子查询：

SELECT p1.id,count(p1.id),p1.postdate
 FROM mytable p1
     LEFT JOIN mytable c1 ON c1.parent_id = p1.id AND p1.parent_id = -1
     LEFT JOIN mytable c2 ON c2.parent_id = c1.id AND p1.parent_id = -1
GROUP BY p1.id,c1.postdate,p1.postdate
ORDER by c1.postdate DESC,p1.postdate DESC

Answer 1

select
 p.id,
 (1+c.n) as parent_post_plus_number_of_subposts,
 p.postdate
from 
    table as p
inner join

    (
    select
    parent_id, count(*) as n, max(postdate) as _postdate
    from table
    group by parent_id
    ) as c

on p.id = c.parent_id
where p.parent_id = -1
order by c._postdate desc

Answer 2

您需要一个递归查询来计算子树中的元素：

WITH RECURSIVE opa AS (
        SELECT id AS par
        , id AS moi
        FROM the_tree
        WHERE parent_id IS NULL
        UNION ALL
        SELECT o.par AS par
        , t.id AS moi
        FROM opa o
        JOIN the_tree t ON t.parent_id = o.moi
        )
SELECT t.id
        , c.cnt
        , t.postdate
FROM the_tree t
JOIN ( SELECT par, COUNT(*) AS cnt
        FROM opa o
        GROUP BY par
        ) c ON c.par = t.id
ORDER BY t.id
        ;

更新（看来 OP 也想要每棵树的最大日期）

        -- The same, but also select the postdate
        -- --------------------------------------
WITH RECURSIVE opa AS (
        SELECT id AS par
        , id AS moi
        , postdate AS postdate
        FROM the_tree
        WHERE parent_id IS NULL
        UNION ALL
        SELECT o.par AS par
        , t.id AS moi
        -- , GREATEST(o.postdate,t.postdate) AS postdate
        , t.postdate AS postdate
        FROM opa o
        JOIN the_tree t ON t.parent_id = o.moi
        )
SELECT t.id
        , c.cnt
        , t.postdate
        , c.maxdate
FROM the_tree t
JOIN ( SELECT par, COUNT(*) AS cnt
        , MAX(o.postdate) AS maxdate -- and obtain the max()
        FROM opa o
        GROUP BY par
        ) c ON c.par = t.id
ORDER BY c.maxdate, t.id
        ;

Answer 3

create table mytable ( id serial primary key, parent_id int references mytable, postdate date );
create index mytable_parent_id_idx on mytable (parent_id);
insert into mytable (id, parent_id, postdate) values (1, null, '2015-03-10');
insert into mytable (id, parent_id, postdate) values (2, 1, '2015-03-11');
insert into mytable (id, parent_id, postdate) values (3, 1, '2015-03-12');
insert into mytable (id, parent_id, postdate) values (4, 3, '2015-03-13');
insert into mytable (id, parent_id, postdate) values (5, null, '2015-03-14');
insert into mytable (id, parent_id, postdate) values (6, null, '2015-03-15');
insert into mytable (id, parent_id, postdate) values (7, 6, '2015-03-16');

with recursive recu as (
  select id as parent, id as root, null::date as child_postdate
    from mytable
   where parent_id is null
   union all
  select r.parent, mytable.id, mytable.postdate
    from recu r
    join mytable
      on parent_id = r.root
)
select m.id, c.cnt, m.postdate, c.max_child_date
  from mytable m
  join ( select parent, count(*) as cnt, max(child_postdate) as max_child_date
           from recu
          group by parent
       ) c on c.parent = m.id
 order by c.max_child_date desc nulls last, m.postdate desc;

Answer 4

看了大家的代码，自己创建了自己需要的子查询。我可以使用 PHP 根据用户的排序选择来改变 'case when' 代码。例如，下面的代码将根据子级别 1 的发布日期对根节点进行排序。

with recursive cte as (
select id as parent, id as root, null::timestamp as child_postdate,0 as depth
from mytable
where parent_id = -1
union all
select r.parent, mytable.id, mytable.postdate,depth+1
from cte r
join mytable
  on parent_id = r.root
)
select m.id, c.cnt, m.postdate
from ssf.dtb_021 m
join ( select parent, count(*) as cnt, max(child_postdate) as max_child_date,depth
       from cte 
      group by parent,depth
     ) c on c.parent = m.id
order by 
  case
    when depth=2 then 1
    when depth=1 then 2
    else 0
  end DESC,
c.max_child_date desc nulls last, m.postdate desc;

postgres 层次结构 - child 级别的计数并按 children 或 grandchildren 的日期排序

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