Php 获取基于类别的随机条目

我有一张叫做“文章”的桌子。此表的结构如下：id（唯一）、类别（文章的类别，即娱乐）、标题（文章的标题）、图像（文章的图像URL）、链接（文章的URL）、计数器（文章的浏览次数）、日期戳（文章发表的日期）

假设我想打印6篇随机娱乐文章。简单但效率较低的方法是这样做

$result = $db->query("SELECT * FROM Articles WHERE category = 'entertainment' ORDER BY RAND() LIMIT 6);

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相反，我该如何更有效地进行？我知道有多个网站解释ORDER BY RAND（）的替代方案，但我不理解这些替代方案。我想根据我的结构来理解。我尝试过多种方法，从洗牌关联数组到创建随机生成器，但都以失败告终，因为我无法让它正常工作。如何在不使用ORDER BY RAND（）的情况下打印出6篇随机娱乐文章？

没有通用的方法，有效的方法之一是根据给定的（可选）标准选择随机数据子集，在您的情况下，

类别

。请注意此列上添加的索引

SELECT
    r1.*
FROM
    articles AS r1
    INNER JOIN (SELECT(RAND() * (SELECT MAX(id) FROM articles)) AS id) AS r2
WHERE
    r1.id >= r2.id
    AND r1.category = 'entertainment'
LIMIT 6;

以下是示例数据（320万行）和执行计划的详细信息：

mysql> SELECT COUNT(*) FROM articles;
+----------+
| COUNT(*) |
+----------+
|  3200000 |
+----------+
1 row in set (0.00 sec)

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希望这对您有所帮助。

您的表大吗（比如说1000多个条目）？如果没有，您可以选择所有数据，并使用PHP在结果中获得一个随机行…@random它现在不大，但将来会变大，所以我现在需要一个解决方案，所以我不必回去修复它。谢谢您的回答！我有一个问题，当你说选择r1时，r1是什么。*？另外，我有7个娱乐项目。我想6随机娱乐文章被准确显示，这个查询有时显示4，5等数字1-6。如果我想准确显示6篇文章，我会怎么做？

mysql> SELECT
    r1.*
FROM
    articles AS r1
    INNER JOIN (SELECT(RAND() * (SELECT MAX(id) FROM articles)) AS id) AS r2
WHERE
    r1.id >= r2.id
    AND r1.category = 'entertainment'
LIMIT 6;
+---------+-------------+-----------------------------------------------------------+---------------+
| id      | topic       | message                                                   | category      |
+---------+-------------+-----------------------------------------------------------+---------------+
| 3153910 | JAX68VVH3FZ | Sed eu eros. Nam consequat dolor                          | entertainment |
| 3153911 | NIY23HWV0VM | tortor. Nunc commodo auctor velit. Aliquam nisl. Nulla eu | entertainment |
| 3153912 | LKQ42FRB7LA | mus. Proin vel nisl. Quisque                              | entertainment |
| 3153913 | PFL39VHI9RM | gravida                                                   | entertainment |
| 3153914 | FGV59TUN9TQ | elit, pellentesque a, facilisis non, bibendum sed,        | entertainment |
| 3153915 | OWH73EBZ1GW | ligula. Nullam enim. Sed nulla ante, iaculis              | entertainment |
+---------+-------------+-----------------------------------------------------------+---------------+
6 rows in set (0.473 sec)

mysql> explain extended 
SELECT
    r1.*
FROM
    articles AS r1
    INNER JOIN (SELECT(RAND() * (SELECT MAX(id) FROM articles)) AS id) AS r2
WHERE
    r1.id >= r2.id
    AND r1.category = 'entertainment'
LIMIT 6;
+----+-------------+------------+--------+-----------------+---------+---------+-------+---------+----------+------------------------------+
| id | select_type | table      | type   | possible_keys   | key     | key_len | ref   | rows    | filtered | Extra                        |
+----+-------------+------------+--------+-----------------+---------+---------+-------+---------+----------+------------------------------+
|  1 | PRIMARY     | <derived2> | system | NULL            | NULL    | NULL    | NULL  |       1 |      100 | NULL                         |
|  1 | PRIMARY     | r1         | ref    | PRIMARY,cat_IDX | cat_IDX | 768     | const | 1560229 |      100 | Using index condition        |
|  2 | DERIVED     | NULL       | NULL   | NULL            | NULL    | NULL    | NULL  | NULL    | NULL     | No tables used               |
|  3 | SUBQUERY    | NULL       | NULL   | NULL            | NULL    | NULL    | NULL  | NULL    | NULL     | Select tables optimized away |
+----+-------------+------------+--------+-----------------+---------+---------+-------+---------+----------+------------------------------+
4 rows in set (0.00 sec)

mysql> SELECT * FROM articles WHERE category = 'entertainment' ORDER BY RAND() LIMIT 6;
+---------+-------------+---------------------------------------------------------------------------+---------------+
| id      | topic       | message                                                                   | category      |
+---------+-------------+---------------------------------------------------------------------------+---------------+
| 2374491 | PZC33VGM0ML | Duis cursus, diam at pretium aliquet, metus urna convallis erat,          | entertainment |
|  382306 | RFN88EPE4MI | malesuada fames ac turpis egestas. Aliquam fringilla cursus purus. Nullam | entertainment |
| 1867986 | KWX30ULB1FR | pede.                                                                     | entertainment |
| 1528863 | ADX52RRJ3MQ | lacus. Mauris non                                                         | entertainment |
| 2188208 | AOD82PXQ6FS | diam luctus lobortis. Class aptent taciti sociosqu ad litora              | entertainment |
|  878426 | ABV08HTB2PG | eu eros. Nam consequat dolor vitae dolor. Donec fringilla. Donec          | entertainment |
+---------+-------------+---------------------------------------------------------------------------+---------------+
6 rows in set (5.726 sec)