[英]MySQL: Query all records that have a given set of relations to another table
是的,有点笨拙,但是我发现很难描述我的问题。 我有以下表格:
id | name
1 | color
2 | material
id | property_id | name
1 | 1 | yellow
2 | 1 | blue
3 | 2 | wood
4 | 2 | stone
id | name
1 | orange juice
2 | cheese
id | substance_id | option_id
1 | 2 | 1
2 | 2 | 3
3 | 1 | 1
现在,我有一个选项列表,想知道哪些物质与所有这些选项有关。 (例如,哪些物质是黄色的并且是木头制成的?)通过一个查询可以做到吗?
我正在Rails中尝试这样做。
就在我脑海中,您可以尝试:
SELECT DISTINCT s.name FROM substances s, relation r
WHERE r.substance_id = s.id
AND r.option_id IN ( 1, 3)
(SELECT s.name FROM substances s, relations r, options o
WHERE r.substance_id = s.id and r.option_id = o.id and o.name='yellow')
INTERSECT
(SELECT s.name FROM substances s, relations r, options o
WHERE r.substance_id = s.id and r.option_id = o.id and o.name='wood')
要么
SELECT s.name FROM substances s
WHERE exists(SELECT * from relations r, options o
WHERE r.substance_id = s.id and r.option_id = o.id and o.name='yellow')
AND exists(SELECT * from relations r, options o
WHERE r.substance_id = s.id and r.option_id = o.id and o.name='wood')
仅使用一个带有property_id
options
表来区分不同类型的选项并不是一个好主意,实际上会使这变得更加困难。 我建议将不同类型的选项分解为不同的表格
MATERIALS(id,name)
COLORS(id,name)
并对每种类型的表使用单独的关系。 在这种情况下,您不需要为每个关系使用单独的表,因为看起来这是一个多(物质)到一个(颜色)关系。
SUBSTANCES(id, name, material_id, color_id)
然后您的查询要简单得多
SELECT s.name FROM substances s, materials m, colors c
WHERE s.color_id = c.id AND m.material_id = m.id
AND m.name = 'wood'
AND c.name = 'yellow'
ActiveRecord应该比前两个更容易处理最后一个查询。
SELECT s.name
FROM substances AS s
LEFT JOIN relations AS r1
ON s.id = r1.substance_id
INNER JOIN relations AS r2
ON r1.substance_id = r2.substance_id
AND r1.option_id < r2.option_id
LEFT JOIN options AS o1
ON o1.id = r1.option_id
LEFT JOIN options AS o2
ON o2.id = r2.option_id
WHERE o1.name = 'yellow'
AND o2.name = 'wood'
我不是很了解如何优化SQL的性能。 您可能要比较上面(与下面)以及此处发布的其他解决方案的基准。
SELECT s.name
FROM substances AS s
LEFT JOIN relations AS r1
ON s.id = r1.substance_id
INNER JOIN relations AS r2
ON r1.substance_id = r2.substance_id
AND r1.option_id < r2.option_id
LEFT JOIN options AS o1
ON o1.id = r1.option_id
AND o1.name = 'wood'
LEFT JOIN options AS o2
ON o2.id = r2.option_id
AND o2.name = 'yellow'
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