Question

我有两张桌子，评分：

+-----------+-----------+-------------+----------+
| rating_id | entity_id | rating_code | position |
+-----------+-----------+-------------+----------+
|         1 |         1 | Quality     |        0 |
|         2 |         1 | Value       |        0 |
|         3 |         1 | Price       |        0 |
+-----------+-----------+-------------+----------+

并且rating_option

+-----------+-----------+------+-------+----------+
| option_id | rating_id | code | value | position |
+-----------+-----------+------+-------+----------+
|         1 |         1 | 1    |     1 |        1 |
|         2 |         1 | 2    |     2 |        2 |
|         3 |         1 | 3    |     3 |        3 |
|         4 |         1 | 4    |     4 |        4 |
|         5 |         1 | 5    |     5 |        5 |
|         6 |         2 | 1    |     1 |        1 |
|         7 |         2 | 2    |     2 |        2 |
|         8 |         2 | 3    |     3 |        3 |
|         9 |         2 | 4    |     4 |        4 |
|        10 |         2 | 5    |     5 |        5 |
|        11 |         3 | 1    |     1 |        1 |
|        12 |         3 | 2    |     2 |        2 |
|        13 |         3 | 3    |     3 |        3 |
|        14 |         3 | 4    |     4 |        4 |
|        15 |         3 | 5    |     5 |        5 |
+-----------+-----------+------+-------+----------+

我需要一个SQL查询（不是应用程序级别，必须保留在数据库中），它将随机选择一组评级。示例结果将如下所示，但会在后续调用中为每个rating_id选择一个随机值：

+-----------+-----------+------+-------+----------+
| option_id | rating_id | code | value | position |
+-----------+-----------+------+-------+----------+
|         1 |         1 | 1    |     1 |        1 |
|         8 |         2 | 3    |     3 |        3 |
|        15 |         3 | 5    |     5 |        5 |
+-----------+-----------+------+-------+----------+

我完全停留在随机部分，到目前为止，通过rating_id进行分组一直是一个废话。任何MySQL忍者想要刺伤吗？

谢谢，乔

编辑：我已经在一堆组合中尝试了rand（），我确信有必要创建结果的随机性，但我无法弄清楚如何为每个组合返回一个随机行评级中的行。我无法使用order by rand() limit 1，因为我需要三行，order by rand() limit 3不会给我一个rating_id，这是最终目标。我需要rand（）和子查询或连接的组合，以便我可以确保每个rating_id之一。

Answer 1

好吧，有点乱，但似乎做了这个工作。有人可能知道他们做得比我做得更好，可以清理它：

SELECT random.rating_id, random.rand_option_id, r3.code, r3.value, r3.position
FROM
    (SELECT r.rating_id,
        (SELECT r2.option_id
         FROM rating_option r2
         WHERE r2.rating_id = r.rating_id
         ORDER BY RAND() LIMIT 1) AS 'rand_option_id'
     FROM rating_option r
     GROUP BY r.rating_id
    ) random
    LEFT JOIN rating_option AS r3 ON r3.option_id = rand_option_id

结果（当然每次都不一样）：

+-----------+----------------+------+-------+----------+
| rating_id | rand_option_id | code | value | position |
+-----------+----------------+------+-------+----------+
|         1 |              4 |    4 |     4 |        4 |
|         2 |              6 |    1 |     1 |        1 |
|         3 |             13 |    3 |     3 |        3 |
+-----------+----------------+------+-------+----------+

Answer 2

您是否查看过rand()函数？

SELECT column FROM table
ORDER BY RAND()
LIMIT 1

http://www.petefreitag.com/item/466.cfm

http://dev.mysql.com/doc/refman/5.0/en/mathematical-functions.html#function_rand

示例代码

select *
from rating_option
group by rating_id
order by rand()

Answer 3

您可以使用rand()功能在评级表中的选择中进行排序。

例如：

select rating_id from rating order by rand() limit 1

Answer 4

正如您的评论和上面的其他帖子所阐明的那样

select * from rating_option order by rand()

将以随机顺序返回所有记录...但是，如果您只想要X号码，那么将其包括为其他人所指出的限制

select * from rating_option order by rand() limit 5 (or whatever number)

从每种类型中选择随机值

4 个答案: