我最近接手了一个10年前创建的老项目。它使用MySQL 5.1。
除此之外，我需要将默认字符集从latin1更改为utf8。
举个例子，我有这样的表格:
CREATE TABLE `users` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`first_name` varchar(45) CHARACTER SET latin1 COLLATE latin1_general_ci DEFAULT NULL,
`last_name` varchar(45) CHARACTER SET latin1 COLLATE latin1_general_ci DEFAULT NULL,
`username` varchar(127) CHARACTER SET latin1 COLLATE latin1_general_ci NOT NULL,
`email` varchar(127) CHARACTER SET latin1 COLLATE latin1_general_ci NOT NULL,
`pass` varchar(20) CHARACTER SET latin1 COLLATE latin1_general_ci NOT NULL,
`active` char(1) CHARACTER SET latin1 COLLATE latin1_general_ci NOT NULL DEFAULT 'Y',
`created` datetime NOT NULL,
`last_login` datetime DEFAULT NULL,
`author` varchar(1) CHARACTER SET latin1 COLLATE latin1_general_ci DEFAULT 'N',
`locked_at` datetime DEFAULT NULL,
`created_at` datetime DEFAULT NULL,
`updated_at` datetime DEFAULT NULL,
`ripple_token` varchar(36) CHARACTER SET latin1 COLLATE latin1_general_ci DEFAULT NULL,
`ripple_token_expires` datetime DEFAULT '2014-10-31 08:03:55',
`authentication_token` varchar(255) CHARACTER SET latin1 COLLATE latin1_general_ci DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `index_users_on_reset_password_token` (`reset_password_token`),
UNIQUE KEY `index_users_on_confirmation_token` (`confirmation_token`),
UNIQUE KEY `index_users_on_unlock_token` (`unlock_token`),
KEY `users_active` (`active`),
KEY `users_username` (`username`),
KEY `index_users_on_email` (`email`)
) ENGINE=InnoDB AUTO_INCREMENT=1677 DEFAULT CHARSET=utf8 CHECKSUM=1 DELAY_KEY_WRITE=1 ROW_FORMAT=DYNAMIC
我设置了自己的Mac来处理这个。没有考虑太多，我运行“brew install mysql”安装mysql 5.7。所以我有一些版本冲突。
我下载了这个数据库的副本并导入了它。
如果我试着像这样运行查询:
ALTER TABLE users MODIFY first_name varchar(45) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL
我得到这个错误:
ERROR 1292 (22007): Incorrect datetime value: '0000-00-00 00:00:00' for column 'created' at row 1
我想我可以用:
ALTER TABLE users MODIFY created datetime NULL DEFAULT '1970-01-01 00:00:00';
Query OK, 0 rows affected (0.06 sec)
Records: 0 Duplicates: 0 Warnings: 0
但我明白:
ALTER TABLE users MODIFY first_name varchar(45) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL ;
ERROR 1292 (22007): Incorrect datetime value: '0000-00-00 00:00:00' for column 'created' at row 1
我必须更新每个值吗?
出现这个问题是因为MYSQL 5.7引入了默认模式，比如
SELECT @@GLOBAL.sql_mode global, @@SESSION.sql_mode session;
=> ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION
在默认模式中，有一个模式NO_ZERO_DATE阻止您在datetime列中放置值0000-00-00 00:00:00。
临时修复将从默认模式中删除模式NO_ZERO_DATE/NO_ZERO_IN_DATE，并保持其他模式不变。
SET GLOBAL sql_mode = 'ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION';
但是一旦你重新启动你的mysql服务器，你所有的临时设置将消失，默认模式将再次启用。要在重新启动时修复此问题，请更改计算机上my.cnf文件中的默认模式。
参考文档:- https://dev.mysql.com/doc/refman/5.7/en/sql-mode.html#:~:text=To%20set%20the%20SQL%20mode,ini%20(Windows)。
我个人的观点:-正确的开发实践应该是在列中放入正确的datetime值，而不是0000-00-00 00:00:00。这样你就不用担心SQL模式了。
我在https://support.plesk.com/hc/en-us/articles/115000666509-How-to-change-the-SQL-mode-in-MySQL上找到了解决方案。我有这个:
mysql> show variables like 'sql_mode';
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+
| Variable_name | Value |
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+
| sql_mode | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set, 1 warning (0.01 sec)
注意上面结果中的NO_ZERO_IN_DATE,NO_ZERO_DATE。我通过这样做去掉了它:
mysql> SET sql_mode = 'ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION';
Query OK, 0 rows affected, 1 warning (0.00 sec)
然后我有了这个:
mysql> show variables like 'sql_mode';
+---------------+--------------------------------------------------------------------------------------------------------------+
| Variable_name | Value |
+---------------+--------------------------------------------------------------------------------------------------------------+
| sql_mode | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+---------------+--------------------------------------------------------------------------------------------------------------+
1 row in set, 1 warning (0.01 sec)
在此之后，我可以成功地使用ALTER TABLE并更改我的表。
