mysql error 1022 is caused by duplicate foreign key names. The solution is: 1. Use the "select * from INFORMATION_SCHEMA.KEY_COLUMN_USAGE where CONSTRAINT_NAME='...'" command to find duplicate foreign key names; 2. Just rename the foreign key name.
The operating environment of this tutorial: Windows 10 system, MySQL version 5.7, Dell G3 computer.
What to do with mysql error 1022?
mysql error Error Code: 1022. Can't write; duplicate key in table `xxx`
Explanation: This error is a duplicate foreign key name
Find duplicate foreign key names, where they are used, the sql is as follows:
select * from INFORMATION_SCHEMA.KEY_COLUMN_USAGE where CONSTRAINT_NAME='重复的外键名称'
If there is no problem, just rename it.
Related expansion:
1 Definition of foreign key
A foreign key is a column in a table that is included in the primary key of another table.
Foreign key is also a type of index, which associates two tables by pointing a column in one table to the primary key in another table.
A table can have one foreign key, or there can be multiple foreign keys that are associated with multiple tables.
2 The role of foreign keys
The main role of foreign keys is to ensure the consistency and integrity of data and reduce data redundancy.
Mainly reflected in the following two aspects:
Prevent execution
Insert a new row from the table, its foreign key value The insertion is blocked if the primary key value is not the main table.
Modify the foreign key value from the table. If the new value is not the primary key value of the main table, the modification is blocked.
Delete a row from the master table, and its primary key value will prevent deletion if it exists in the slave table (if you want to delete it, you must first delete the relevant rows from the slave table).
The primary table modifies the primary key value. If the old value exists in the secondary table, the modification is prevented (if you want to modify it, you must first delete the relevant rows from the secondary table).
Cascade execution
Delete rows from the main table and delete related rows from the table together.
Modify the primary key value of the main table, and modify the foreign key value of the related rows of the slave table together.
3 Foreign key creation restrictions
The parent table must already exist in the database, or be the table currently being created.
If the latter is the case, the parent table and the child table are the same table. Such a table is called a self-referential table, and this structure is called self-referential integrity.
The primary key must be defined for the parent table.
The number of columns in the foreign key must be the same as the number of columns in the primary key of the parent table.
The two tables must be InnoDB tables. MyISAM tables do not currently support foreign keys.
Foreign key columns must be indexed. MySQL 4.1.2 and later versions will automatically create indexes when establishing foreign keys, but in earlier versions, they need to be created explicitly.
The columns of the two tables in the foreign key relationship must have similar data types, that is, columns that can be converted to each other. For example, int and tinyint can be used, but int and char cannot.
Recommended learning: "MySQL Video Tutorial"
The above is the detailed content of What to do with mysql error 1022. For more information, please follow other related articles on the PHP Chinese website!