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 `table`WHERE 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;

反馈

实测 38万数据，随机取10条 1 可以随机取值，执行时间1-2秒。 2 运行超过20秒没反应，试了3次。 3 取的10条数据是连续的ID，执行0.001秒。 4 随机取10条，id在1-4000之间，执行0.003秒，试了10次以上。 5 随机取10条，id在1-4000之间，执行0.003秒，试了10次以上。 6 取的10条数据是连续的ID，执行0.001秒。

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