How to modify enum type values of fields in MySQL

1： Background description

mysql The database has the following table structure , What we need to pay attention to status Type of field , This time, the requirement is that you want to set the enumeration value of this field to error Changed to: initialize_failed

mysql> desc servers;
+-------------------+--------------------------------------------------------+------+-----+--------------+-------+
| Field             | Type                                                   | Null | Key | Default      | Extra |
+-------------------+--------------------------------------------------------+------+-----+--------------+-------+
| id                | varchar(36)                                            | NO   | PRI | NULL         |       |
| name              | varchar(36)                                            | NO   |     | NULL         |       |
| gw_id             | varchar(36)                                            | NO   |     | NULL         |       |
| client_ip_pool    | varchar(36)                                            | NO   |     | NULL         |       |
| eip_id            | varchar(36)                                            | YES  |     | NULL         |       |
| proto             | enum('UDP')                                            | YES  |     | UDP          |       |
| status            | enum('initializing','initialized','error')             | YES  |     | initializing |       |
| port              | int(11)                                                | NO   |     | NULL         |       |
| compress          | tinyint(1)                                             | YES  |     | NULL         |       |
| url               | varchar(512)                                           | YES  |     | NULL         |       |
| created_at        | datetime                                               | YES  |     | NULL         |       |
| updated_at        | datetime                                               | YES  |     | NULL         |       |
| deleted_at        | datetime                                               | YES  |     | NULL         |       |
| deleted           | bigint(20)                                             | YES  |     | NULL         |       |
+-------------------+--------------------------------------------------------+------+-----+--------------+-------+

2： Problem analysis

The first thing to mention is , The project on which this table depends has been running for some time , That is, there are certain data in the table , Probably status Property already has error Data exists for , After all, you suddenly change the type of a field , It must also mean that the source code of the project has also been changed here ,db In this table, this field appears error The data is understandable . So for safety , Query the... In this table status The status of the field

mysql> select * from vpn_servers where initialize_status = 'error' limit 2;
Empty set (0.00 sec)

mysql> select distinct initialize_status from vpn_servers;
+-------------------+
| initialize_status |
+-------------------+
| initialized       |
| initializing      |
+-------------------+
2 rows in set (0.00 sec)

It's a surprise , The value of this field in this table does not error Of , Then there are two ways to modify the enumeration value of this field .
（1） Modify table structure directly , Redefine the enum type value .
（2） Modify table structure , Add the enumeration type value initialize_failed, Then the original error Is changed to initialize_failed, Finally, redefine the enumeration value and delete error
Be careful ： If there is this in this table error The data of , Then we must go the way 2, If you want to go the way 1, Then, it is better to balance the production environment with the test environment , Is it safe to delete this status have error The data of , Whether this table has foreign keys with other tables ？ Cascade delete Association ？, If you want to delete , Be sure to pass api To delete , In case of db, Dirty data is left in the cache .

3： Problem solving

Method （1）： Because in this example, I found that there is no information about this in this table status Field has error The data of , So the diagram is convenient , Can be modified directly

alter table servers modify `status` enum ('initializing','initialized','initialize_failed') default 'initializing';

** Method （2）** Start talking about methods 2 front , Imagine the following , If the table contains error The data of , As shown below

MariaDB [test_using]> select * from servers where status = 'error' \G
*************************** 1. row ***************************
            id: 12345
          name: test
         gw_id: 11111
client_ip_pool: NULL
        eip_id: 22222
        status: error
1 row in set (0.00 sec)

At this time in status Field has error In the case of data , Think again like a method 1 That way, direct changes will occur Unpredictable problems , In this case , Direct change , Leading to the original error The data of becomes empty directly （ No null）, In this case, if it is a production environment , A small screw problem may lead to a series of major accidents .

MariaDB [test_using]> alter table servers modify `status` enum ('initializing','initialized','initialize_failed') default 'initializing';
Query OK, 1 row affected, 1 warning (0.02 sec)     
Records: 1  Duplicates: 0  Warnings: 1

MariaDB [test_using]> select * from servers where status = 'error' \G
Empty set (0.00 sec)

MariaDB [test_using]> 
MariaDB [test_using]> 
MariaDB [test_using]> select * from servers  \G
*************************** 1. row ***************************
            id: 12345
          name: test
         gw_id: 11111
client_ip_pool: NULL
        eip_id: 22222
        status: 
1 row in set (0.00 sec)

therefore , The correct and safe way is as follows
Check the table first enum Add a new type value to the field

alter table servers modify `status` enum ('initializing','initialized','error','initialize_failed') default 'initializing';

next update This table , Replace the original type value to be replaced error The data of becomes the new type value ’initialize_failed’

update servers set status = 'initialize_failed' where status = 'error';

Last , Change the table again status Of enum Type value of , Get rid of error

alter table servers modify `status` enum ('initializing','initialized','initialize_failed') default 'initializing';

After querying data

MariaDB [test_using]> select * from servers  \G
*************************** 1. row ***************************
            id: 12345
          name: test
         gw_id: 11111
client_ip_pool: NULL
        eip_id: 22222
        status: initialize_failed
1 row in set (0.00 sec)

4： Postscript

In fact, there is another method that is not recommended , That is to delete the table and rebuild , Applicable to offline environment , Or when the data in the table is garbage data , It doesn't hurt to delete it .