mysql order by rand() 优化方法

mysql order by rand() 优化方法

mysql> select * from user order by rand() limit 1;
+-------+------------+----------------------------------+----------+--------------+-----------+
| id    | phone      | password                         | salt     | country_code | ip        |
+-------+------------+----------------------------------+----------+--------------+-----------+
| 15160 | 6549721306 | e4f302120c006880a247b652ad0e42f2 | 40343586 | 86           | 127.0.0.1 |
+-------+------------+----------------------------------+----------+--------------+-----------+
1 row in set (0.25 sec)
mysql> explain select * from user order by rand() limit 1;
+----+-------------+-------+------+---------------+------+---------+------+--------+---------------------------------+
| id | select_type | table | type | possible_keys | key  | key_len | ref  | rows   | Extra                           |
+----+-------------+-------+------+---------------+------+---------+------+--------+---------------------------------+
|  1 | SIMPLE      | user  | ALL  | NULL          | NULL | NULL    | NULL | 200303 | Using temporary; Using filesort |
+----+-------------+-------+------+---------------+------+---------+------+--------+---------------------------------+
1 row in set (0.00 sec)

<?php// 获取总记录数$sqlstr = 'select count(*) as recount from user';$query = mysql_query($sqlstr) or die(mysql_error());$stat = mysql_fetch_assoc($query);$total = $stat['recount'];// 随机偏移$offset = mt_rand(0, $total-1);// 偏移后查询$sqlstr = 'select * from user limit '.$offset.',1';$query = mysql_query($sqlstr) or die(mysql_error());$result = mysql_fetch_assoc($query);print_r($result);?>

mysql> select * from user limit 23541,1;+-------+------------+----------------------------------+----------+--------------+-----------+| id    | phone      | password                         | salt     | country_code | ip        |+-------+------------+----------------------------------+----------+--------------+-----------+| 23542 | 3740507464 | c8bc1890de179538d8a49cc211859a46 | 93863419 | 86           | 127.0.0.1 |+-------+------------+----------------------------------+----------+--------------+-----------+1 row in set (0.01 sec)mysql> explain select * from user limit 23541,1;+----+-------------+-------+------+---------------+------+---------+------+--------+-------+| id | select_type | table | type | possible_keys | key  | key_len | ref  | rows   | Extra |+----+-------------+-------+------+---------------+------+---------+------+--------+-------+|  1 | SIMPLE      | user  | ALL  | NULL          | NULL | NULL    | NULL | 200303 | NULL  |+----+-------------+-------+------+---------------+------+---------+------+--------+-------+1 row in set (0.00 sec)