Question

是否可以使联接表的行成为主查询的字段名称和值？让我通过显示结构和数据来解释这一点：

structs
    id
    type

struct_fields
    id
    struct_id
    name
    value

示例数据：

structs
    1, faq
    2, faq
    3, post

struct_fields
    1, 1, "question", "Will there be food?" 
    2, 1, "answer", "No, you will have to bring your own food"
    3, 1, "active", 1
    4, 2, "question", "Will there be drinks?"
    5, 2, "answer", "Yes, there will be plenty of drinks"
    6, 2, "active", 0
    7, 3, "title", "Great post!"
    8, 3, "body", "Lorum ipsum..."
    9, 3, "published", "2019-01-01 23:12:00"

这将为我提供常见类型的所有结构，以及所有对应的字段

SELECT s.*, f.*
FROM `structs` s
RIGHT JOIN `struct_fields` f ON f.struct_id = s.id
WHERE s.type = 'faq'

但是显然我的行中有双打，因为所有也会生成行的struct_fields

但是当我添加

GROUP BY s.id

仅显示匹配的struct_fields的第一行（phpmyadmin），并带有struct_fields的字段名称。

我希望能够选择具有所有相应struct_fields的所有结构，其中struct_fields名称将是结果中的字段名称，而struct_field值为该值，以便能够使用HAVING进行选择子选择。所以：

结果：

id, type, question,                answer,          active
1,  faq,  "Will there be food?",   "No, you...",    1
2,  faq,  "Will there be drinks?", "Yes, there...", 0

所以现在我可以使用以下内容扩展查询：

如果是常见问题，例如：HAVING active = 1 (or WHERE active = 1)

如果是帖子，例如：WHERE published > DATE_SUB(NOW(), INTERVAL 1 DAY)

Answer 1

您可以尝试以下操作-使用conditional aggregation and Join

select s.id,s.type,question, answer, active from FROM `structs` s
inner join
(
select struct_id, max(case when name='question' then value end) as question,
max(case when name='answer' then value end) as answer,
max(case when name='active' then value end) as active
from struct_fields group by struct_id
)f ON f.struct_id = s.id WHERE s.type = 'faq'

使联接表的行成为主查询的字段名称和值？

1 个答案: