我需要从最新的新闻数据库中随机抽取 4 个条目。
由于该表有很多行，使用 RAND() 排序或浪费资源这样做是否明智？因为它将遍历整个表格并重新排序。
有没有更好的方法，从数百行的表中提取随机特征项？
示例：
$l=$database->query("SELECT car,price,thumbnail FROM cardb WHERE type='new' order by RAND() LIMIT 4");
foreach($l as $l){print_r($l);}
感谢您花时间回答 }
【问题讨论】：
标签： php mysql mysql-management
嗯...我会在两个查询中执行此操作。获取随机行号：
SELECT
floor(count * rand()) r1,
floor(count * rand()) r2,
floor(count * rand()) r3,
floor(count * rand()) r4
FROM
(SELECT count(*) count FROM cardb WHERE type = 'new') c
并获取行：
SELECT car, price, thumbnail FROM cardb WHERE type = 'new' LIMIT {r1}, 1
UNION ALL
SELECT car, price, thumbnail FROM cardb WHERE type = 'new' LIMIT {r2}, 1
UNION ALL
SELECT car, price, thumbnail FROM cardb WHERE type = 'new' LIMIT {r3}, 1
UNION ALL
SELECT car, price, thumbnail FROM cardb WHERE type = 'new' LIMIT {r4}, 1
【讨论】：
ORDER BY RAND() 不会。