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使用"insert into"语句进行数据库操作时可能遇到主键冲突，用户需要根据应用场景进行忽略或者覆盖等操作。总结下，有三种解决方案来避免出错。
测试表：
CREATE TABLE `device` (
`devid` mediumint(8) unsigned NOT NULL AUTO_INCREMENT,
`status` enum(‘alive‘,‘dead‘,‘down‘,‘readonly‘,‘drain‘) DEFAULT NULL,
`spec_char` varchar(11) DEFAULT ‘0‘,
PRIMARY KEY (`devid`)
) ENGINE=InnoDB
1. insert ignore into
遇主键冲突，保持原纪录，忽略新插入的记录。
mysql> select * from device ; +-------+--------+-------------+ | devid | status | spec_char | +-------+--------+-------------+ | 1 | dead | zhonghuaren | | 2 | dead | zhong | +-------+--------+-------------+ 2 rows in set (0.00 sec) mysql> insert into device values (1,‘alive‘,‘yangting‘); ERROR 1062 (23000): Duplicate entry ‘1‘ for key ‘PRIMARY‘ mysql> insert ignore into device values (1,‘alive‘,‘yangting‘); Query OK, 0 rows affected (0.00 sec) mysql> select * from device ; +-------+--------+-------------+ | devid | status | spec_char | +-------+--------+-------------+ | 1 | dead | zhonghuaren | | 2 | dead | zhong | +-------+--------+-------------+ 2 rows in set (0.00 sec)
可见 insert ignore into当遇到主键冲突时，不更改原纪录，也不报错
2. replace into
遇主键冲突，替换原纪录，即先删除原纪录，后insert新纪录
mysql> replace into device values (1,‘alive‘,‘yangting‘); Query OK, 2 rows affected (0.00 sec) mysql> select * from device ; +-------+--------+-----------+ | devid | status | spec_char | +-------+--------+-----------+ | 1 | alive | yangting | | 2 | dead | zhong | +-------+--------+-----------+ 2 rows in set (0.00 sec)
3. insert into ... ON DUPLICATE KEY UPDATE
其实这个是原本需要执行3条SQL语句（SELECT,INSERT,UPDATE），缩减为1条语句即可完成。
即
IF (SELECT * FROM where 存在) { UPDATE SET WHERE ; } else { INSERT INTO; }
如：mysql>
insert into device values (1,‘readonly‘,‘yang‘) ON DUPLICATE KEY UPDATE status =‘drain‘; Query OK, 2 rows affected (0.00 sec)
上面语句伪代码表示即为
if (select * from device where devid=1) { update device set status =‘drain‘ where devid=1 } else { insert into device values (1,‘readonly‘,‘yang‘) }
很明显，devid=1 是有的，这样就执行update操作
mysql> select * from device ; +-------+--------+-----------+ | devid | status | spec_char | +-------+--------+-----------+ | 1 | drain | yangting | | 2 | dead | zhong | +-------+--------+-----------+ 2 rows in set (0.00 sec)
如果更新多条记录可以向下面这样写
insert into device values(1, "dead", "ccc") ON DUPLICATE KEY UPDATE status =‘drain‘, spec_char = "cccc"
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原文地址：http://www.cnblogs.com/phpfans/p/4648694.html
