错误代码：1451 有 2 个主键

Question

我不能运行以下语句：

delete from UT_Session where my_id='5146' and upgrade_time='2016-01-03 17:25:18'

自从我得到：

Error Code: 1451. Cannot delete or update a parent row: a foreign key constraint fails (`Upgrade_tool`.`pre_tasks`, CONSTRAINT `pre_tasks_ibfk_1` FOREIGN KEY (`my_id`) REFERENCES `UT_Session` (`my_id`))

有以下表格：

create table UT_Session
(
my_id int not null,
upgrade_time DATETIME not null,
ownerName varchar(20),
source varchar(20) not null,
target varchar(20) not null,
isClosed boolean,
primary key (my_id,upgrade_time)
)ENGINE=INNODB;

CREATE INDEX upgrate_time_index
ON UT_Session (upgrade_time);

create table pre_tasks
(
    my_id int,
    foreign key (my_id) references UT_Session(my_id),
    upgrade_time DATETIME not null,
    foreign key (upgrade_time) references UT_Session(upgrade_time),
    pre_task_type varchar (100),
    reason varchar(500),
    primary key (my_id,pre_task_type,upgrade_time)
)ENGINE=INNODB;


create table post_tasks
(
    my_id int,
    foreign key (my_id) references UT_Session(my_id),
    upgrade_time DATETIME not null,
    foreign key (upgrade_time) references UT_Session(upgrade_time),
    post_task_type varchar (100),
    reason varchar(500),
    primary key (my_id,post_task_type,upgrade_time)
)ENGINE=INNODB;

现在当我运行查询显示表格的内容时，我得到：

mysql> select * from UT_Session where my_id='5146';
+------+---------------------+-----------+----------+----------+----------+
| my_id | upgrade_time        | ownerName | source   | target   | isClosed |
+------+---------------------+-----------+----------+----------+----------+
| 5146 | 2016-01-03 17:25:18 | Ronen     | 5.1.2.12 | 5.2.2.26 |        0 |
| 5146 | 2016-01-03 17:35:10 | Ronen     | 5.1.2.12 | 5.2.2.26 |        0 |
| 5146 | 2016-01-03 17:36:57 | Ronen     | 5.1.2.12 | 5.2.2.26 |        1 |
+------+---------------------+-----------+----------+----------+----------+

mysql> select * from pre_tasks  where my_id='5146';
+------+---------------------+--------------------------------------------------------+--------+
| my_id | upgrade_time        | pre_task_type                                         | reason |
+------+---------------------+--------------------------------------------------------+--------+
| 5146 | 2016-01-03 17:36:57 | Type 87954r0f                                                                          |        |
| 5146 | 2016-01-03 17:36:57 | Type 1a79F4rf                                                                          |        |
+------+---------------------+--------------------------------------------------------+--------+

mysql> select * from post_tasks  where my_id='5146';
+------+---------------------+--------------------------------------------------------+--------+
| my_id | upgrade_time        | post_task_type                                        | reason |
+------+---------------------+--------------------------------------------------------+--------+
| 5146 | 2016-01-03 17:36:57 | Type v7d54r8f                                                                          |        |
+------+---------------------+--------------------------------------------------------+--------+

如您所见，"my_id" 和 "upgrade_time" 都是键，我要删除的行不存在于子表中，因为时间不同。

这是怎么回事？

谢谢！

Answer 1

是的，但您确实在子项中有记录或使用 my_id='5146' 引用了 table，因此它会正确抛出该错误。如果您真的想删除该记录，请先从子 table 中删除它们，然后再从父

中删除它们

您可以使用 ON DELETE CASCADE 级联选项创建 FOREIGN KEY 约束，下面说 delete 也会级联到子级 table

foreign key (my_id) references UT_Session(my_id) on delete cascade

您实际上想做的是创建一个复合外键，如下所示；在这种情况下，记录的唯一性将取决于这两个键。

FOREIGN KEY (my_id, upgrade_time)  
  REFERENCES UT_Session (my_id, upgrade_time) ON DELETE CASCADE

错误代码：1451 有 2 个主键

Error code: 1451 with 2 primary keys

mysql

primary-key

mysql-error-1451