通过要求许多满足条件来过滤一对多查询

本文介绍了通过要求许多满足条件来过滤一对多查询的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

想象一下以下表格:

创建表格框(id int，名称文本，...)；

create table boxes( id int, name text, ...);

创建表Thingsinboxes(id int，box_id int，事物枚举('apple，'banana'，'orange');

create table thingsinboxes( id int, box_id int, thing enum('apple,'banana','orange');

表格如下:


Boxes:
id | name
1  | orangesOnly
2  | orangesOnly2
3  | orangesBananas
4  | misc

thingsinboxes:
id | box_id | thing
1  |  1     | orange
2  |  1     | orange
3  |  2     | orange
4  |  3     | orange
5  |  3     | banana
6  |  4     | orange
7  |  4     | apple
8  |  4     | banana

如何选择至少包含一个橙色并且没有一个不是橙色的框?

How do I select the boxes that contain at least one orange and nothing that isn't an orange?

假设我有几十万个盒子，可能还有一百万个盒子，那么这个比例如何变化?

How does this scale, assuming I have several hundred thousand boxes and possibly a million things in boxes?

如果可能的话，我希望将其全部保留在SQL中，而不是使用脚本对结果集进行后处理.

I'd like to keep this all in SQL if possible, rather than post-processing the result set with a script.

我同时使用了postgres和mysql，因此子查询可能很糟糕，因为mysql不会优化子查询(无论如何，都是6版之前的版本).

I'm using both postgres and mysql, so subqueries are probably bad, given that mysql doesn't optimize subqueries (pre version 6, anyway).

推荐答案

SELECT b.*
FROM boxes b JOIN thingsinboxes t ON (b.id = t.box_id)
GROUP BY b.id
HAVING COUNT(DISTINCT t.thing) = 1 AND SUM(t.thing = 'orange') > 0;

这是另一种不使用GROUP BY的解决方案:

Here's another solution that does not use GROUP BY:

SELECT DISTINCT b.*
FROM boxes b
  JOIN thingsinboxes t1
    ON (b.id = t1.box_id AND t1.thing = 'orange')
  LEFT OUTER JOIN thingsinboxes t2
    ON (b.id = t2.box_id AND t2.thing != 'orange')
WHERE t2.box_id IS NULL;

一如既往，在得出关于查询的可伸缩性或性能的结论之前，您必须使用现实的数据集进行尝试，并测量性能.

As always, before you make conclusions about the scalability or performance of a query, you have to try it with a realistic data set, and measure the performance.

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Subqueries