mysql实现随机获取几条数据的方法

sql语句有几种写法
1：SELECT * FROM tablename ORDER BY RAND() LIMIT 想要获取的数据条数；

2：SELECT *FROM table WHERE id >= (SELECT FLOOR( MAX(id) * RAND()) FROM table ) ORDER BY id LIMIT 想要获取的数据条数;

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 想要获取的数据条数;

4：SELECT * FROM tableWHERE id >= (SELECT floor(RAND() * (SELECT MAX(id) FROM table))) ORDER BY id LIMIT 想要获取的数据条数;

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 想要获取的数据条数;

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 想要获取的数据条数;

1的查询时间>>2的查询时间>>5的查询时间>6的查询时间>4的查询时间>3的查询时间，也就是3的效率最高。