提高mysql随机查询的效率

1. 基本使用:
   SELECT * FROM `table` ORDER BY RAND() LIMIT 0,10;
   但是在ORDER BY后面用到RAND(),查询速度非常慢.


2. MAX()*RAND()提高效率
   SELECT * FROM `table`
WHERE id >= (SELECT floor( RAND() * ((SELECT MAX(id) FROM `table`)-(SELECT MIN(id) FROM `table`)) + (SELECT MIN(id) FROM `table`)))
ORDER BY id LIMIT 1;


3. JOIN
   SELECT *
FROM `table` AS t1 JOIN (SELECT ROUND(RAND() * ((SELECT MAX(id) FROM `table`)-(SELECT MIN(id) FROM `table`))+(SELECT MIN(id) FROM `table`)) AS id) AS t2
WHERE t1.id >= t2.id
ORDER BY t1.id LIMIT 1;

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• 转载自 http://www.ruofeel.cn/