Add Auto-Increment ID to existing table?

问题

I have a pre-existing table, containing \'fname\', \'lname\', \'email\', \'password\' and \'ip\'. But now I want an auto-increment column. However, when I enter:

ALTER TABLE users
ADD id int NOT NULL AUTO_INCREMENT

I get the following:

#1075 - Incorrect table definition; there can be only one auto column and it must be defined as a key

Any advice?:)

回答1:

Try this

ALTER TABLE `users` ADD `id` INT NOT NULL AUTO_INCREMENT PRIMARY KEY

回答2:

If you don't care whether the auto-id is used as PRIMARY KEY, you can just do

ALTER TABLE `myTable` ADD COLUMN `id` INT AUTO_INCREMENT UNIQUE FIRST;

I just did this and it worked a treat.

回答3:

If you want to add AUTO_INCREMENT in an existing table, need to run following SQL command:

 ALTER TABLE users ADD id int NOT NULL AUTO_INCREMENT primary key

回答4:

First you have to remove the primary key of the table

ALTER TABLE nametable DROP PRIMARY KEY

and now yo can add the autoincrement ...

ALTER TABLE nametable ADD id INT NOT NULL AUTO_INCREMENT PRIMARY KEY

回答5:

Well, you must first drop the auto_increment and primary key you have and then add yours, as follows:

-- drop auto_increment capability
alter table `users` modify column id INT NOT NULL;
-- in one line, drop primary key and rebuild one
alter table `users` drop primary key, add primary key(id);
-- re add the auto_increment capability, last value is remembered
alter table `users` modify column id INT NOT NULL AUTO_INCREMENT;

回答6:

Delete the primary key of a table if it exists:

 ALTER TABLE `tableName` DROP PRIMARY KEY;

Adding an auto-increment column to a table :

ALTER TABLE `tableName` ADD `Column_name` INT PRIMARY KEY AUTO_INCREMENT;

Modify the column which we want to consider as the primary key:

alter table `tableName` modify column `Column_name` INT NOT NULL AUTO_INCREMENT PRIMARY KEY;

回答7:

If you run the following command :

ALTER TABLE users ADD id int NOT NULL AUTO_INCREMENT PRIMARY KEY;

This will show you the error :

ERROR 1060 (42S21): Duplicate column name 'id'

This is because this command will try to add the new column named id to the existing table.

To modify the existing column you have to use the following command :

ALTER TABLE users MODIFY id int NOT NULL AUTO_INCREMENT PRIMARY KEY;

This should work for changing the existing column constraint....!

回答8:

Just change the ADD to MODIFY and it will works !

Replace

ALTER TABLE users ADD id int NOT NULL AUTO_INCREMENT

ALTER TABLE users MODIFY id int NOT NULL AUTO_INCREMENT;

回答9:

ALTER TABLE users ADD id int NOT NULL AUTO_INCREMENT primary key FIRST

回答10:

ALTER TABLE users CHANGE id int( 30 ) NOT NULL AUTO_INCREMENT

the integer parameter is based on my default sql setting have a nice day

回答11:

Check for already existing primary key with different column. If yes, drop the primary key using:

ALTER TABLE Table1
DROP CONSTRAINT PK_Table1_Col1
GO

and then write your query as it is.

回答12:

ALTER TABLE `table` ADD `id` INT NOT NULL AUTO_INCREMENT unique

Try this. No need to drop your primary key.

回答13:

Proceed like that :

Make a dump of your database first

Remove the primary key like that

ALTER TABLE yourtable DROP PRIMARY KEY

Add the new column like that

ALTER TABLE yourtable add column Id INT NOT NULL AUTO_INCREMENT FIRST, ADD primary KEY Id(Id)

The table will be looked and the AutoInc updated.

来源：https://stackoverflow.com/questions/14753321/add-auto-increment-id-to-existing-table

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mysql

sql

definition

auto-increment