mysql隨機取數據的幾種高效率方法

我用最簡單的也是常用的方法來看看，下面再介紹高效的mysql隨機數據的方法，有需要的朋友可以參考一下。

1]普通方法, 效率太低

SELECT * FROM table ORDER BY rand() LIMIT 10;

[2] JOIN的方法：

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 10;

再把語句完善一下，加上MIN(id)的判斷。我在最開始測試的時候，就是因為沒有加上MIN(id)的判斷，結果有一半的時間總是查詢到表中的前面幾行。
完整查詢語句是：

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;
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;

前者花費時間 0.147433 秒
後者花費時間 0.015130 秒
都是查詢10咨物。