表结构:CREATE TABLE test_rand(id int(11) AUTO_INCREMENT PRIMARY KEY,c2 varchar(30) DEFAULT NULL, c3 date DEFAULT NULL);
插入800W条记录;
随机取一条记录:(id已建立索引)
SELECT * FROM test_rand order by rand() limit 1;
mysql> select * from test_rand order by rand() limit 1;
+---------+--------------------+------------+
| id | c2 | c3 |
+---------+--------------------+------------+
| 1399866 | testing partitions | 1996-10-21 |
+---------+--------------------+------------+
1 row in set (19.13 sec)
第一次优化:
SELECT FLOOR(MAX(id)*RAND()) FROM test_rand
+-----------------------+
| FLOOR(MAX(id)*RAND()) |
+-----------------------+
| 446373 |
+-----------------------+
1 row in set (2.20 sec)
再次优化:
mysql> select FLOOR(id*rand()) from test_rand where id=(select MAX(id) from test
_rand);
+------------------+
| FLOOR(id*rand()) |
+------------------+
| 5225551 |
+------------------+
1 row in set (0.00 sec)