1

我有以下表格（简化）：

CREATE TABLE groups
 ( id PRIMARY KEY, 
   path ltree,
   ... 
 );

CREATE TABLE items
 ( id bigserial, 
   path ltree,
   ... 
   PRIMARY KEY (id, path)
 );

对于每个项目，都有一个该项目所属的组列表。组由其完整路径表示。最多可能有 10M 个项目，每个项目属于大约 20 个组。

我需要设计以下查询。给定 (a) 一个“父”组和 (b) 最多 10 个附加组的列表，找到“父”组的直接后代，它们的子树中至少有一个项目包含在搜索条件。

例如，给定父组“NorthAmerica.USA”和其他组 [“CandyLovers.ChocolateLovers”、“Athletes.Footballers”]，如果存在“George”这样的项目，则“NorthAmerica.USA.CA”是一个结果那是在像[“NorthAmerica.USA.CA.LosAngeles”，“Athletes.Footballers”，“CandyLovers.ChocolateLovers.ChocolateDonutLovers”这样的组中

我尝试了几种不同的方法来编写查询，但它们的扩展性很差：需要几分钟才能在搜索条件中返回一组 1M 项和 3-4 条路径的结果。例如：

    EXPLAIN ANALYZE
    SELECT *
    FROM groups
    WHERE path ~ CAST ('1.2.22' || '.*{1}' AS lquery)
          AND EXISTS
          (SELECT 1
           FROM
             (SELECT array_agg(DISTINCT leaf_paths_sans_result_path.path) AS paths_of_a_match,
                     max(path_count) AS path_count
              FROM items,

                (SELECT path,
                   count(*) OVER() AS path_count
                 FROM (
                        VALUES (groups.path) , ('1.3'),('1.4')) t (path)) leaf_paths_sans_result_path
              WHERE 1 = 1
                    AND items.path <@ leaf_paths_sans_result_path.path
              GROUP BY id) items_by_id
           WHERE cardinality(paths_of_a_match) = path_count );

结果如下：

     Index Scan using idx_groups__path__gist on groups  (cost=0.28..37013.74 rows=38 width=469) (actual time=11.735..322285.421 rows=950 loops=1)
       Index Cond: (path ~ '1.2.22.*{1}'::lquery)
       Filter: (SubPlan 1)
       Rows Removed by Filter: 3
       SubPlan 1
         ->  Subquery Scan on items_by_id  (cost=0.55..1809359.86 rows=3752 width=0) (actual time=338.162..338.162 rows=1 loops=953)
               ->  GroupAggregate  (cost=0.55..1809322.34 rows=3752 width=65) (actual time=338.159..338.159 rows=1 loops=953)
                     Group Key: ibt.id
                     Filter: (cardinality(array_agg(DISTINCT "*VALUES*".column1)) >= max(3))
                     Rows Removed by Filter: 7845
                     ->  Nested Loop  (cost=0.55..1809228.54 rows=3752 width=65) (actual time=0.044..307.087 rows=20423 loops=953)
                           Join Filter: (ibt.path <@ "*VALUES*".column1)
                           Rows Removed by Join Filter: 651228
                           ->  Index Scan using idx_items__id on items  (cost=0.55..1752954.06 rows=1250543 width=193) (actual time=0.007..110.517 rows=223884 loops=953)
                           ->  Materialize  (cost=0.00..0.05 rows=3 width=32) (actual time=0.000..0.000 rows=3 loops=213361141)
                                 ->  Values Scan on "*VALUES*"  (cost=0.00..0.04 rows=3 width=32) (actual time=0.002..0.003 rows=3 loops=953)
     Planning time: 3.151 ms
     Execution time: 322286.404 ms
    (18 rows)

我可以根据需要更改数据模型以优化此查询。我正在运行 PostgreSQL v9.5

非常感谢！对不起一个混乱的问题。

4

1 回答 1

0

看起来你正在使用ltree 模块？以下查询避免了中间array_agg数组：

select  *
from    items i
join    groups g
on      i.groups = g.id
where   g.path ~ '1.2.22.*' and
        (
             i.path ~ '*.1.3.*' or
             i.path ~ '*.1.4.*'
        )
group by
        g.id
having  count(distinct
        case
        when i.path ~ '*.1.3.*' then 1
        when i.path ~ '*.1.4.*' then 2
        end) = 2

这些count构造断言两个条件都满足，而不仅仅是匹配相同模式的两行。

于 2018-03-26T09:23:46.227 回答