查询 MYSQL post_meta 为 table 的新格式

Question

嗨，我有一个现有的 table，它是

post_meta

----------------------------------------------------------------
| meta_id  | post_id      | meta_key   | meta_value            |
----------------------------------------------------------------
|  1       | 1            | field1     | John Doe              |
|  2       | 1            | field2     | jonedoe@gmail.com     |
|  3       | 1            | field3     | 099999999             |
|  4       | 2            | field1     | Err ManMa             |
|  5       | 2            | field2     | errmanma@gmail.com    |
|  6       | 2            | field3     | 09231412312           |
----------------------------------------------------------------

如何创建或格式化我的 post_meta table？

----------------------------------------------------------------
| meta_id  | field1    | field2             | field3            |
----------------------------------------------------------------
|  1       | John Doe  | jonedoe@gmail.com  | 099999999         |
|  2       | Err ManMa | errmanma@gmail.com | 09231412312       |
----------------------------------------------------------------

感谢您的帮助

Answer 1

我认为你的结果列应该是 post_id, field1, field2, field3 然后这是一个 table 关键问题，试试这个：

select
    post_id,
    max(case when meta_key = 'field1' then meta_value end) as field1,
    max(case when meta_key = 'field2' then meta_value end) as field2,
    max(case when meta_key = 'field3' then meta_value end) as field3
from post_meta
-- where meta_key in ('field1', 'field2', 'field3')
group by post_id
-- having coalesce(field1, field2, field3) is not null

SQLFiddle Demo

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