如何修改MariaDB表中Varchar的“主键”列的大小？

Question

I have

Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 5
Server version: 10.0.36-MariaDB-0ubuntu0.16.04.1 Ubuntu 16.04

My table desc:

MariaDB [GTX_CC]> desc SubscribedUser;
+---------------------------------------------+--------------+------+-----+---------+-------+
| Field                                       | Type         | Null | Key | Default | Extra |
+---------------------------------------------+--------------+------+-----+---------+-------+
| UserID                                      | varchar(25)  | NO   | PRI | NULL    |       |
| UserName                                    | varchar(100) | YES  |     | NULL    |       |
| UserStatusCode                              | varchar(10)  | NO   |     | NULL    |       |
| Password                                    | varchar(512) | NO   |     | NULL    |       |

Now I want to Modify the Column length of UserID to varchar(999)

Running

MariaDB [GTX_CC]> ALTER TABLE SubscribedUser MODIFY UserID  varchar(999) NOT NULL  AUTO_INCREMENT;

gives the following error:

ERROR 1063 (42000): Incorrect column specifier for column 'UserID'

Added>

I also tried:

MariaDB [GTX_CC]> ALTER TABLE SubscribedUser MODIFY UserID  varchar(999) NOT NULL ;

It also gives error as:

ERROR 1071 (42000): Specified key was too long; max key length is 767 bytes

Also Tried as follows:

MariaDB [GTX_CC]> ALTER TABLE SubscribedUser MODIFY UserID  varchar(767) NOT NULL ;
ERROR 1071 (42000): Specified key was too long; max key length is 767 bytes
MariaDB [GTX_CC]> ALTER TABLE SubscribedUser MODIFY UserID  varchar(766) NOT NULL ;
ERROR 1071 (42000): Specified key was too long; max key length is 767 bytes
MariaDB [GTX_CC]> 

What wrong in my statement? Any help , please?

Answer 1

What is wrong, appears to be related to this question: MariaDB won't create table with large VARCHAR as PRIMARY KEY .

In summary, and without wanting to repeat what's said in the above link, there is a maximum length for varchar primary keys, and the limit depends on the charset. To verify that, drop the primary key ( alter table SubscribedUser drop primary key ), alter the length of userid to your 999 (that succeeds), try to add userid as primary key ( alter table SubscribedUser add primary key(userid) ) and it'd fail with the same error.

Answer 2

The script will be as follows:

LOCK TABLES 
UserSession WRITE,
SubscribedUser WRITE;

ALTER TABLE UserSession
DROP FOREIGN KEY fk_Session_SubscribedUser1,
MODIFY SubscribedUser_UserID varchar(255) NOT NULL;

ALTER TABLE SubscribedUser MODIFY UserID  varchar(255) NOT NULL ;

ALTER TABLE UserSession
ADD CONSTRAINT fk_Session_SubscribedUser1 FOREIGN KEY (SubscribedUser_UserID)
REFERENCES SubscribedUser (UserID);

UNLOCK TABLES;

The maximum allowed char length under varchar is 255 only.

Answer 3

Please provide SHOW CREATE TABLE SubscribedUser . I question whether that 'describe' is correct. It should be impossible to have a VARCHAR as an AUTO_INCREMENT , regardless of the length .

Decide whether you want the PRIMARY KEY to be AUTO_INCREMENT or VARCHAR .

If you choose to have a VARCHAR , then think about what size is reasonable.

If you need to index a large VARCHAR , then see http://mysql.rjweb.org/doc.php/limits#767_limit_in_innodb_indexes for the options you have.