当FOREIGN_KEY_CHECKS = 0且执行了2个查询时，我发生了一个奇怪的错误（除了FOREIGN_CHECK_CHECKS之外，两种情况都相同。
错误导致错误ERROR 1823（HY000）：无法添加外键约束...（下面的完整错误）
如果我使用SET FOREIGN_KEY_CHECKS = 1运行查询，它将按预期工作。 （这几乎似乎是关键词，因为关闭外键检查应该让事情发生，但不应该这样做）
这是mysql中的错误还是我不理解？我找不到关于这个mysql错误代码的很多信息。
MYSQL VERISON： 33年6月5日
错误（最后查询）：
mysql> SET FOREIGN_KEY_CHECKS=0;
Query OK, 0 rows affected (0.00 sec)
mysql> ALTER TABLE phppos_people ADD INDEX phppos_people_ibfk_1 (image_id);
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> ALTER TABLE phppos_customers ADD CONSTRAINT phppos_customers_ibfk_1 FOREIGN KEY person_id (person_id) REFERENCES phppos_people (person_id) ON UPDATE NO ACTION ON DELETE NO ACTION;
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> ALTER TABLE phppos_employees ADD CONSTRAINT phppos_employees_ibfk_1 FOREIGN KEY person_id (person_id) REFERENCES phppos_people (person_id) ON UPDATE NO ACTION ON DELETE NO ACTION;
ERROR 1823 (HY000): Failed to add the foreign key constraint 'migrate/person_id' to system tables
SUCCESS：
mysql> SET FOREIGN_KEY_CHECKS=1;
Query OK, 0 rows affected (0.00 sec)
mysql> ALTER TABLE phppos_people ADD INDEX phppos_people_ibfk_1 (image_id);
Query OK, 0 rows affected (0.04 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> ALTER TABLE phppos_customers ADD CONSTRAINT phppos_customers_ibfk_1 FOREIGN KEY person_id (person_id) REFERENCES phppos_people (person_id) ON UPDATE NO ACTION ON DELETE NO ACTION;
Query OK, 1 row affected (0.03 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> ALTER TABLE phppos_employees ADD CONSTRAINT phppos_employees_ibfk_1 FOREIGN KEY person_id (person_id) REFERENCES phppos_people (person_id) ON UPDATE NO ACTION ON DELETE NO ACTION;
Query OK, 1 row affected (0.04 sec)
Records: 1 Duplicates: 0 Warnings: 0
SCHEMA：
mysql> show create table phppos_people;
+---------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+---------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| phppos_people | CREATE TABLE `phppos_people` (
`first_name` varchar(255) CHARACTER SET ucs2 NOT NULL,
`last_name` varchar(255) CHARACTER SET ucs2 NOT NULL,
`phone_number` varchar(255) CHARACTER SET ucs2 NOT NULL,
`email` varchar(255) CHARACTER SET ucs2 NOT NULL,
`address_1` varchar(255) CHARACTER SET ucs2 NOT NULL,
`address_2` varchar(255) CHARACTER SET ucs2 NOT NULL,
`city` varchar(255) CHARACTER SET ucs2 NOT NULL,
`state` varchar(255) CHARACTER SET ucs2 NOT NULL,
`zip` varchar(255) CHARACTER SET ucs2 NOT NULL,
`country` varchar(255) CHARACTER SET ucs2 NOT NULL,
`comments` text CHARACTER SET ucs2 NOT NULL,
`image_id` int(11) DEFAULT NULL,
`person_id` int(11) NOT NULL,
PRIMARY KEY (`person_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+---------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> show create table phppos_customers;
+------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| phppos_customers | CREATE TABLE `phppos_customers` (
`id` int(11) NOT NULL,
`person_id` int(11) NOT NULL,
`account_number` varchar(255) CHARACTER SET ucs2 DEFAULT NULL,
`override_default_tax` int(11) NOT NULL,
`company_name` varchar(255) CHARACTER SET ucs2 NOT NULL,
`balance` decimal(23,10) NOT NULL,
`credit_limit` decimal(23,10) DEFAULT NULL,
`points` decimal(23,10) NOT NULL,
`current_spend_for_points` decimal(23,10) NOT NULL,
`current_sales_for_discount` int(11) NOT NULL,
`taxable` int(11) NOT NULL,
`tax_certificate` varchar(255) CHARACTER SET ucs2 NOT NULL,
`cc_token` varchar(255) CHARACTER SET ucs2 DEFAULT NULL,
`cc_preview` varchar(255) CHARACTER SET ucs2 DEFAULT NULL,
`card_issuer` varchar(255) CHARACTER SET ucs2 DEFAULT NULL,
`tier_id` int(11) DEFAULT NULL,
`deleted` int(11) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
答案 0 :(得分：1)
是的，这似乎是一个错误。我可以在MySQL 5.6+中验证它（在MySQL 8中类似），而5.5不受影响。这里的问题是MySQL使用的约束名称。
中[CONSTRAINT [symbol]] FOREIGN KEY [index_name] (index_col_name, ...) REFERENCES tbl_name (index_col_name,...)
约束名称应为 symbol ，如果没有给出，则自动创建：
如果给出了CONSTRAINT符号子句，则符号值（如果使用）在数据库中必须是唯一的。重复的符号将导致类似于以下的错误：ERROR 1022（2300）：无法写入;表格中的重复键＃sql- 464_1＆＃39;。如果未给出该子句，或者CONSTRAINT关键字后面不包含符号，则会自动创建约束的名称。
这通常会这样：
如果您为FOREIGN_KEY_CHECKS禁用ALTER TABLE，但CREATE TABLE禁用person_id，则会另外使用 index_name ：
因此，虽然 index_name 通常只需要对每个表都是唯一的，但是这里，两个ALTER语句中的公共 index_name person_id将是导致麻烦，因为MySQL试图用相同（错误）的名称创建两个约束。
作为一种解决方法，在您的情况下，您可以从alter语句中删除 index_name ALTER TABLE phppos_customers ADD INDEX person_id (person_id);
ALTER TABLE phppos_customers ADD CONSTRAINT FOREIGN KEY (person_id) REFERENCES ...
，因为如果一切正常，索引应该得到< em> symbol 无论如何：
如果子表上已经显式定义了可以支持外键的索引，则忽略index_name值。否则，MySQL会隐式创建一个根据以下规则命名的外键索引：
如果已定义，则使用CONSTRAINT符号值。否则，使用FOREIGN KEY index_name值。
如果既未定义CONSTRAINT符号也未定义FOREIGN KEY index_name，则使用引用外键列的名称生成外键索引名称。
如果要显式命名索引，但使用默认约束名称，则可以在添加外键之前添加索引，例如：使用
FOREIGN_KEY_CHECKS MySQL 8显示略有不同的行为（当ALTER TABLE被禁用且仅 PolylineOptions lineOptions = null;
lineOptions = new PolylineOptions();
lineOptions.addAll(points);
lineOptions.width(5);
lineOptions.color(Color.RED);
Polyline polyline = mGoogleMap.addPolyline(lineOptions);
polyline.remove();
时）：它也错误地使用 index_name ，但仅当没有时给出符号 - 在您的情况下可以使用，因为您设置了符号。
答案 1 :(得分：0)
得到相同的错误编号：1823；符号：ER_FK_FAIL_ADD_SYSTEM； SQLSTATE: HY00063 消息：无法将外键约束“%s”添加到系统表
在我的情况下，当我减少查询工作的约束名称的长度时，FK 名称太长。