[mysql] Add Auto-Increment ID to existing table?

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?:)

Just change the ADD to MODIFY and it will works !

Replace

ALTER TABLE users ADD id int NOT NULL AUTO_INCREMENT

To

ALTER TABLE users MODIFY id int NOT NULL AUTO_INCREMENT;

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

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

Try this. No need to drop your primary key.

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.

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;

Try this

ALTER TABLE `users` ADD `id` INT NOT NULL AUTO_INCREMENT;

for an existing primary key

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

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

For PostgreSQL you have to use SERIAL instead of auto_increment.

ALTER TABLE your_table_name ADD COLUMN id SERIAL NOT NULL PRIMARY KEY

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.

This SQL request works for me :

ALTER TABLE users
CHANGE COLUMN `id` `id` INT(11) NOT NULL AUTO_INCREMENT ;

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

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.

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;

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....!