如何在组成表上进行交集

问题描述

我有一个具有多对多关系的简单SQL关系模型.这是组成表

I have a simple SQL relational model with a many to many relation. Here is the composition table

 ___________________________
| object1_id  | object2_id  |
|---------------------------|

我想知道一组object2共有的所有object1.我的基本感觉是发出这样的请求

I would like to know all the object1 that are common to a set of object2. My basic feeling is to do a request like this

SELECT c.object1_id FROM composition c WHERE c.object2_id = <given_id_1>
INTERSECT
SELECT c.object1_id FROM composition c WHERE c.object2_id = <given_id_2>

如果我在集合中有N个object2，我将做N个INTERSECT

And if I have N object2 in the set, I'll do N INTERSECT

SELECT c.object1_id FROM composition c WHERE c.object2_id = <given_id_1>
INTERSECT
SELECT c.object1_id FROM composition c WHERE c.object2_id = <given_id_2>
...
INTERSECT
SELECT c.object1_id FROM composition c WHERE c.object2_id = <given_id_N>

但是，它看起来并没有非常优化.你能帮助我吗 ?我不是SQL专家.我想我可以使用JOIN来做到这一点.

However, it doesn't look very optimized. Can you help me ? I am not really a SQL expert. I think I could use a JOIN to do that.

样品

 ___________________________
| object1_id  | object2_id  |
|---------------------------|
|         10  |           1 |
|         11  |           1 |
|         10  |           2 |
|         12  |           2 |
|         10  |           3 |
|         11  |           3 |
|         13  |           3 |

示例

• {object2_id set} => {预期object1_id}
• {1，2} => {10}
• {1，3} => {10，11}
• {1，2，3} => {10}

• { object2_id set } => { expected object1_id }
• { 1, 2 } => { 10 }
• { 1, 3 } => { 10, 11 }
• { 1, 2, 3 } => { 10 }

推荐答案

在性能方面，您的查询看起来还可以.您是否进行过测量以查看是否确实存在问题?

In terms of performance your query looks OK. Have you measured it to see if there really is a problem?

如果(object1_id, object2_id)是唯一的，则可以更简洁地编写查询，如下所示:

If (object1_id, object2_id) is unique then you can write the query more concisely as follows:

SELECT object1_id
FROM composition
WHERE object2_id IN (id1, id2, ..., id6)
GROUP BY object1_id
HAVING COUNT(*) = 6

请注意，6是提供的ID的数量.如果提供了不同数量的ID，则应对此进行更改.您必须测量您的dadta上的实际性能，以查看这是否可以提高速度.

Note that the 6 is the number of provided IDs. This should be changed if a different number of IDs is provided. You would have to measure the actual performance on your dadta to see if this gives any speed increase.

如果您不能假设唯一性，那么这应该起作用:

If you can't assume uniqueness then this should work:

SELECT object1_id
FROM composition
WHERE object2_id IN (id1, id2, ..., id6)
GROUP BY object1_id
HAVING COUNT(DISTINCT object2_id) = 6

最重要的是确保您的桌子上有适当的索引！这比您编写一个查询还是另一个查询更重要.

The most important thing though is to make sure you have appropriate indexes on your table! This is far more important than whether you write one query or the other.

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