查询具有多个 AND 和 OR 条件的连接表

Question

我需要在 Rails 中构建一个查询，返回具有特定属性集的人。我简化了我的例子。所以这里有两张表：

Table: people
+----+----------+
| id |   name   |
+----+----------+
|  1 | Person A |
|  2 | Person B |
|  3 | Person C |
+----+----------+

Table: attributes
+----+-----------+--------+--------+
| id | person_id |  name  | value  |
+----+-----------+--------+--------+
|  1 |         1 | age    | 32     |
|  2 |         1 | gender | male   |
|  3 |         2 | age    | 16     |
|  4 |         2 | gender | male   |
|  5 |         3 | gender | female |
+----+-----------+--------+--------+

person_id 是对表people 中一个人的引用。

在我的查询中，我想（例如）提出以下问题：

1. 把所有 25 岁以上的男性都给我！

   name = 'gender' AND value = 'male' 和 name = 'age' AND value > '25' 应该返回 1 条记录 (person_id=1)

2. 把所有男性或 25 岁以上的人都给我！

   name = 'gender' AND value = 'female' 或 name = 'age' AND value > '25' 应该返回 2 条记录 (person_id=1 and 3)

示例 2 并不难做到。但是我对示例 1 有疑问。我不知道如何处理这里的 AND。不要忘记：WHERE 语句是动态的。意味着可以有很多，也可以只有一个。

基本上，我正在寻找正确的 SQL 语句来执行此操作。我已经玩了一点，到目前为止我得到的最好的东西是：

SELECT people.* 
FROM people 
INNER JOIN attributes ON attributes.person_id = people.id 
WHERE
  attributes.name = 'gender' AND attributes.value = 'male' OR 
  attributes.name = 'age' AND attributes.value > '25' 
GROUP BY people.id 
HAVING count(*) = 2

我不喜欢这个解决方案，因为我必须在HAVING 子句中指定匹配数。必须有更优雅、更灵活的解决方案才能做到这一点。

下面是一个更复杂但不起作用的例子：

SELECT people.* 
FROM people 
INNER JOIN attributes ON attributes.person_id = people.id 
WHERE
  (attributes.name = 'gender' AND attributes.value = 'male') OR 
  (attributes.name = 'age' AND attributes.value > '25') AND
  (attributes.name = 'bodysize' AND attributes.value > '180')
GROUP BY people.id

我们将不胜感激任何想法和帮助。谢谢！

Answer 1

考虑类似

SELECT people.* 
FROM people
LEFT JOIN attributes AS attr_gender
    ON attr_gender.person_id = people.id 
    AND attr_gender.name = 'gender'
LEFT JOIN attributes AS attr_age
    ON attr_age.person_id = people.id 
    AND attr_age.name = 'age'

结合：

1)

SELECT ...
WHERE attr_gender.value = 'male'
AND attr_age.value::int > 25

2)

SELECT ...
WHERE attr_gender.value = 'male'
OR attr_age.value::int > 25

注意：强制转换是必要的 - '9' > '25'。

Answer 2

你试过了吗：

(attributes.name = 'gender' AND attributes.value = 'male') OR
(attributes.name = 'age' AND attributes.value > '25')

没有“GROUP BY”/“HAVING”部分？