【轉】mysql實現隨機獲取幾條數據的方法

sql語句有幾種寫法

1：SELECT * FROM tablename ORDER BY RAND() LIMIT 想要獲取的數據條數；

2：SELECT *FROM `table` WHERE id >= (SELECT FLOOR( MAX(id) * RAND()) FROM `table` ) ORDER BY id LIMIT 想要獲取的數據條數;

3：SELECT * FROM `table`  AS t1 JOIN (SELECT ROUND(RAND() * (SELECT MAX(id) FROM `table`)) AS id) AS t2 WHERE t1.id >= t2.id
ORDER BY t1.id ASC LIMIT 想要獲取的數據條數;

4：SELECT * FROM `table`WHERE id >= (SELECT floor(RAND() * (SELECT MAX(id) FROM `table`))) ORDER BY id LIMIT 想要獲取的數據條數;

5：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 想要獲取的數據條數;

6：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 想要獲取的數據條數;

1的查詢時間>>2的查詢時間>>5的查詢時間>6的查詢時間>4的查詢時間>3的查詢時間，也就是3的效率最高。

 

轉 https://blog.csdn.net/xionglangs/article/details/50630758