Question

我需要在Rails中构建一个返回具有一组特定属性的人的查询。我简化了我的榜样。所以这是两个表：

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中某人的引用。

在我的查询中，我想（例如）提出以下问题：

给我所有年龄超过25岁的男性！

name = 'gender' AND value = 'male'和name = 'age' AND value > '25'应返回1条记录(person_id=1)
给我所有男性或25岁以上的人！

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

示例2并不那么难。但我在示例1中遇到了问题。我不知道如何在这里处理AND。不要忘记：WHERE语句是动态的。意味着可以有一堆，或只有一个。

基本上我正在寻找合适的SQL语句来做到这一点。我已经玩了一点点，直到现在我做的最好的事情就是：

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。必须有一个更优雅和灵活的解决方案来做到这一点。

这是一个不复杂的例子：

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

任何想法和帮助将不胜感激。谢谢！

Answer 1

考虑类似

的内容

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：必须进行投射 - '9' > '25'。

Answer 2

你试过这个：

（attributes.name ='gender'AND attributes.value ='male'）或
（attributes.name ='age'AND attributes.value＆gt; '25'）

没有“GROUP BY”/“HAVING”部分？

使用多个AND和OR条件查询连接表

2 个答案: