Postgresql 如何查找上面有多个标记的项目? 问题:
我有一个名为Postgresql 如何查找上面有多个标记的项目? 问题:,postgresql,many-to-many,relational-division,Postgresql,Many To Many,Relational Division,我有一个名为item\u tag\u assn的表,它映射带有标记的项目(多对多关联表)。我需要找出应用了一组标签的项目。例如,如果我的表包含以下数据: item_id | tag_id ------------------ 205 | 110 206 | 120 207 | 130 205 | 130 206 | 147 210 | 110 205 | 152 209 | 111 210 | 177
item\u tag\u assn
的表,它映射带有标记的项目(多对多关联表)。我需要找出应用了一组标签的项目。例如,如果我的表包含以下数据:
item_id | tag_id
------------------
205 | 110
206 | 120
207 | 130
205 | 130
206 | 147
210 | 110
205 | 152
209 | 111
210 | 177
205 | 147
212 | 110
212 | 135
205 | 135
212 | 147
------------------
如果我在寻找
- 标记为110、135和147的项目,然后我希望结果集中有项目205和项目212李>
- 标记为110、130、135、147和152的项目,那么我应该只获得项目205,因为只有项目205具有与之关联的所有标记
环境:
- PostgreSQL 9.5
- 我不允许在此表中添加第三列或创建新表
迄今取得的进展: 我找到了这样的解决方案:
SELECT DISTINCT ita1.item_id
FROM
item_tag_assn AS ita1
LEFT JOIN
item_tag_assn AS ita2 ON ita1.item_id = ita2.item_id
LEFT JOIN
item_tag_assn AS ita3 ON ita2.item_id = ita3.item_id
GROUP BY ita1.item_id
HAVING
sum((ita1.tag_id = 110 and ita2.tag_id = 135 and ita3.tag_id = 147)::integer) >= 1
而且它可以工作
需要优化 关联表相当大。将其与自身连接起来成本高昂,速度较慢,而且扩展性不强。我认为窗口功能会有所帮助,但我不知道如何使用它们
有没有更好的方法来解决这个问题?如果我理解正确,您需要这样的东西:
WITH search AS (
SELECT '{110,130,135,147,152}'::int4[] as search
), searched AS (
SELECT DISTINCT item_id,
tag_id
FROM item_tag_assn
JOIN search ON (tag_id) = ANY(search)
ORDER BY 1, 2
), aggregated AS (
SELECT item_id,
array_agg(tag_id) AS agg
FROM searched
GROUP BY 1
)
SELECT *
FROM aggregated, search
WHERE agg = search
;
search
-用于设置搜索的数组(数组必须预先排序)。
已搜索
-已搜索标记以外的所有行
聚合
-聚合在数组中每个项目的标记\u id\u id
您可以将agg=search
更改为agg@>search
,之后不需要在searched
中进行预排序和排序
从问题中添加数据集时:
WITH item_tag_assn AS (
SELECT 205 as item_id, 110 as tag_id
UNION SELECT 206 , 120
UNION SELECT 207 , 130
UNION SELECT 205 , 130
UNION SELECT 206 , 147
UNION SELECT 210 , 110
UNION SELECT 205 , 152
UNION SELECT 209 , 111
UNION SELECT 210 , 177
UNION SELECT 205 , 147
UNION SELECT 212 , 110
UNION SELECT 212 , 135
UNION SELECT 205 , 135
UNION SELECT 212 , 147
),search AS (
SELECT '{110,130,135,147,152}'::int4[] as search
), searched AS (
SELECT DISTINCT item_id,
tag_id
FROM item_tag_assn
JOIN search ON (tag_id) = ANY(search)
ORDER BY 1, 2
), aggregated AS (
SELECT item_id,
array_agg(tag_id) AS agg
FROM searched
GROUP BY 1
)
SELECT *
FROM aggregated, search
WHERE agg = search
;
结果:
item_id | agg | search
---------+-----------------------+-----------------------
205 | {110,130,135,147,152} | {110,130,135,147,152}
(1 row)
如果将搜索更改为“{110135147}”
:
item_id | agg | search
---------+---------------+---------------
212 | {110,135,147} | {110,135,147}
205 | {110,135,147} | {110,135,147}
(2 rows)
要在产品上运行,您需要在项目标签assn(标签id)上创建索引创建索引代码>
由于某些原因,它没有按预期工作:-\n它总是返回一个空白集。您能运行我的测试示例吗?该示例工作正常。我确实检查了我的桌子,它也在那里工作。我不知道为什么它在第一次尝试时不起作用。我认为这个对我来说足够有效。谢谢:)
QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------------------
Hash Join (cost=32.72..35.34 rows=1 width=68) (actual time=0.055..0.059 rows=3 loops=1)
Hash Cond: (aggregated.agg = search.search)
CTE search
-> Result (cost=0.00..0.01 rows=1 width=32) (actual time=0.001..0.001 rows=1 loops=1)
CTE searched
-> Unique (cost=27.73..28.55 rows=110 width=8) (actual time=0.029..0.031 rows=3 loops=1)
-> Sort (cost=27.73..28.00 rows=110 width=8) (actual time=0.029..0.029 rows=3 loops=1)
Sort Key: x.item_id, x.tag_id
Sort Method: quicksort Memory: 25kB
-> Nested Loop (cost=10.40..24.00 rows=110 width=8) (actual time=0.013..0.014 rows=3 loops=1)
-> CTE Scan on search search_1 (cost=0.00..0.02 rows=1 width=32) (actual time=0.002..0.002 rows=1 loops=1)
-> Bitmap Heap Scan on x (cost=10.40..22.88 rows=110 width=8) (actual time=0.009..0.009 rows=3 loops=1)
Recheck Cond: (tag_id = ANY (search_1.search))
Heap Blocks: exact=1
-> Bitmap Index Scan on i1 (cost=0.00..10.38 rows=110 width=0) (actual time=0.002..0.002 rows=3 loops=1)
Index Cond: (tag_id = ANY (search_1.search))
CTE aggregated
-> HashAggregate (cost=2.75..4.12 rows=110 width=36) (actual time=0.038..0.039 rows=3 loops=1)
Group Key: searched.item_id
-> CTE Scan on searched (cost=0.00..2.20 rows=110 width=8) (actual time=0.029..0.031 rows=3 loops=1)
-> CTE Scan on aggregated (cost=0.00..2.20 rows=110 width=36) (actual time=0.040..0.043 rows=3 loops=1)
-> Hash (cost=0.02..0.02 rows=1 width=32) (actual time=0.005..0.005 rows=1 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 9kB
-> CTE Scan on search (cost=0.00..0.02 rows=1 width=32) (actual time=0.000..0.001 rows=1 loops=1)
Planning time: 0.309 ms
Execution time: 0.115 ms