Question

假设我有以下架构：

艺术家：

    +------------+------------------+------+-----+---------+----------------+
    | Field      | Type             | Null | Key | Default | Extra                  |
    +------------+------------------+------+-----+---------+----------------+
    | id         | int(10) unsigned | NO   | PRI | NULL    | auto_increment |                   |
    | name       | varchar(255)     | YES  | UNI | NULL    |                |
    +------------+------------------+------+-----+---------+----------------+

事件：

+------------+------------------+------+-----+---------+----------------+
| Field      | Type             | Null | Key | Default | Extra              |
+------------+------------------+------+-----+---------+----------------+
| id         | int(10) unsigned | NO   | PRI | NULL    | auto_increment     |
| date       | timestamp        | YES  |     | NULL    |                |
| artist_id  | int(11)          | YES  |     | NULL    |                |
| venue_id   | int(11)          | YES  |     | NULL    |                |
+------------+------------------+------+-----+---------+----------------+

资产：

+---------------------+------------------+------+-----+---------+----------------+
| Field               | Type             | Null | Key | Default | Extra          |
+---------------------+------------------+------+-----+---------+----------------+
| id                  | int(10) unsigned | NO   | PRI | NULL    | a
| event_id            | int(11)          | YES  |     | NULL    |                 
| source_asset_title  | varchar(255)     | YES  |     | NULL    |                |
| source_created_time | timestamp        | YES  |     | NULL    |                |

我希望给定artist.id的每个事件都有 4个资产的结果集，按事件日期排序，例如：

+----------+----------+------------------------------------------------------------------------------------------------------------------------+---------------------+---------------------+
| event_id | asset_id | source_asset_title                                                                                                     | event_date          | date                |
+----------+----------+------------------------------------------------------------------------------------------------------------------------+---------------------+---------------------+
|        1 |     2089 | aba                                                                                                                       | 2015-12-03 07:00:00 | 2015-12-03 07:00:00 |
|        1 |     2101 | abb                                                                                                                        | 2015-12-03 07:00:00  | 2011-04-07 15:30:00 |
|        1 |     2102 | abc                                                                                                                    | 2015-12-03 07:00:00  | 2011-05-22 16:00:00 |
|        1 |     2107 | abd                                                                                                                     | 2015-12-03 07:00:00  | 2011-06-11 15:00:00 |
|        2 |     2109 | abe                                                                                                                     | 2011-07-18 15:00:00  | 2011-07-18 15:00:00 |
|        2 |     2113 | abf                                                                                                                    | 2011-07-18 15:00:00  | 2011-07-24 15:30:00 |
|        2 |     2115 | abg                                                                                                                    | 2011-07-18 15:00:00  | 2011-08-25 16:00:00 |
|        2 |     2123 | abh                                                                                                                    | 2011-07-18 15:00:00  | 2011-08-28 16:00:00 |
|        3 |     2126 | abi                                                                                                                    | 2011-09-01 16:00:00  | 2011-09-01 16:00:00 |
|        3 |     2129 | abj                                                                                                                    | 2011-09-01 16:00:00  | 2011-09-10 16:00:00 |
|        3 |     2135 | abk                                                                                                                    | 2011-09-01 16:00:00  | 2011-10-14 16:00:00 |
|        3 |     2147 | abl                                                                                                                    | 2011-09-01 16:00:00  | 2011-10-22 16:00:00 |

如果每个事件没有一个子查询，我怎么能实现这个目标呢？

我相信这里的模式和结果集使得它与StackExchange上的其他问题的不同之处在于新问题是合适的。

Answer 1

以下是artist.id = 1的SQL，由events.date

从较新到较旧排序

SELECT
  events.id as event_id,
  assets.id as asset_id,
  source_asset_title
FROM assets
INNER JOIN events ON events.id = assets.event_id
INNER JOIN artists ON artists.id = events.artist_id
WHERE artists.id = 1
ORDER BY events.date DESC

Answer 2

不，没有子查询就无法实现指定的结果集。作为替代方案，请考虑GROUP_CONCAT，但您可能需要增加MySQL的group_concat_max_len的大小以包含您要描述的所有列。这可能是也可能不是一个好主意。

每个关系选择前N个项目，每个项目一行

2 个答案: