# sql – Alter a MySQL column to be AUTO_INCREMENT

## The Question :

203 people think this question is useful

I’m trying to modify a table to make its primary key column AUTO_INCREMENT after the fact. I have tried the following SQL, but got a syntax error notification.

ALTER TABLE document
ALTER COLUMN document_id AUTO_INCREMENT



Am I doing something wrong or is this not possible?

+--------------------+
| VERSION()          |
+--------------------+
| 5.0.75-0ubuntu10.2 |
+--------------------+


388 people think this answer is useful
ALTER TABLE document MODIFY COLUMN document_id INT auto_increment



78 people think this answer is useful

Roman is right, but note that the auto_increment column must be part of the PRIMARY KEY or a UNIQUE KEY (and in almost 100% of the cases, it should be the only column that makes up the PRIMARY KEY):

ALTER TABLE document MODIFY document_id INT AUTO_INCREMENT PRIMARY KEY



11 people think this answer is useful

In my case it only worked when I put not null. I think this is a constraint.

ALTER TABLE document MODIFY COLUMN document_id INT NOT NULL AUTO_INCREMENT;



8 people think this answer is useful

The SQL to do this would be:

ALTER TABLE document MODIFY COLUMN document_id INT AUTO_INCREMENT;



There are a couple of reasons that your SQL might not work. First, you must re-specify the data type (INT in this case). Also, the column you are trying to alter must be indexed (it does not have to be the primary key, but usually that is what you would want). Furthermore, there can only be one AUTO_INCREMENT column for each table. So, you may wish to run the following SQL (if your column is not indexed):

ALTER TABLE document MODIFY document_id INT AUTO_INCREMENT PRIMARY KEY;



7 people think this answer is useful

You must specify the type of the column before the auto_increment directive, i.e. ALTER TABLE document MODIFY COLUMN document_id INT AUTO_INCREMENT.

6 people think this answer is useful

AUTO_INCREMENT is part of the column’s datatype, you have to define the complete datatype for the column again:

ALTER TABLE document
ALTER COLUMN document_id int AUTO_INCREMENT



(int taken as an example, you should set it to the type the column had before)

5 people think this answer is useful

You can use the following query to make document_id to increment automatically

ALTER TABLE document MODIFY COLUMN document_id INT auto_increment



It is preferred to make document_id primary key as well

ALTER TABLE document MODIFY COLUMN document_id INT auto_increment PRIMARY KEY;



5 people think this answer is useful

You can do it like this:

 alter table [table_name] modify column [column_name] [column_type] AUTO_INCREMENT;



3 people think this answer is useful

AUTO_INCREMENT is part of the column’s datatype, you have to define the complete datatype for the column again:

ALTER TABLE document
MODIFY COLUMN document_id int AUTO_INCREMENT



(int taken as an example, you should set it to the type the column had before)

3 people think this answer is useful

Below statement works. Note that you need to mention the data type again for the column name (redeclare the data type the column was before).

ALTER TABLE document
MODIFY COLUMN document_id int AUTO_INCREMENT;



3 people think this answer is useful

If none of the above works try this. This is what I did in MYSQL and yes, you need to write the column name (document_id) twice.

ALTER TABLE document
CHANGE COLUMN document_id document_id INT(11) NOT NULL AUTO_INCREMENT ;



2 people think this answer is useful

To modify the column in mysql we use alter and modify keywords. Suppose we have created a table like:

create table emp(
id varchar(20),
ename varchar(20),
salary float
);



Now we want to modify type of the column id to integer with auto increment. You could do this with a command like:

alter table emp modify column id int(10) auto_increment;



2 people think this answer is useful

Previous Table syntax:

CREATE TABLE apim_log_request (TransactionId varchar(50) DEFAULT NULL);



For changing the TransactionId to auto increment use this query

ALTER TABLE apim_log_request MODIFY COLUMN TransactionId INT auto_increment;



2 people think this answer is useful
alter table tbl_user MODIFY COLUMN id int(10) auto_increment;



2 people think this answer is useful

Just like this:

alter table document modify column id int(11) auto_increment;

1 people think this answer is useful

As you are redefining the column again, you have to specify the datatype again and add auto_increment to it as it’s a part of datatype.

ALTER TABLE document MODIFY COLUMN document_id INT AUTO_INCREMENT;



1 people think this answer is useful

## Setting column as primary key and auto_increment at the same time:

  mysql> ALTER TABLE persons MODIFY COLUMN personID INT auto_increment PRIMARY KEY;
Query OK, 10 rows affected (0.77 sec)
Records: 10  Duplicates: 0  Warnings: 0

mysql>



0 people think this answer is useful

Try the following:

ALTER TABLE table_name MODIFY COLUMN id datatype auto_increment;



0 people think this answer is useful

You can apply the atuto_increment constraint to the data column by the following query:

ALTER TABLE customers MODIFY COLUMN customer_id BIGINT NOT NULL AUTO_INCREMENT;



But, if the columns are part of a foreign key constraint you, will most probably receive an error. Therefore, it is advised to turn off foreign_key_checks by using the following query:

SET foreign_key_checks = 0;



Therefore, use the following query instead:

SET foreign_key_checks = 0;
ALTER TABLE customers MODIFY COLUMN customer_id BIGINT NOT NULL AUTO_INCREMENT;
SET foreign_key_checks = 1;



0 people think this answer is useful

Since SQL tag is attached to the question I really think all answers missed one major point.

MODIFY command does not exist in SQL server So you will be getting an error when you run the

ALTER TABLE Satellites MODIFY COLUMN SatelliteID INT auto_increment PRIMARY KEY;

In this case you can either add new column as INT IDENTITY

ALTER TABLE Satellites
CONSTRAINT PK_YourTable PRIMARY KEY CLUSTERED;



### OR

Fill the existing null index with incremental numbers using this method,
DECLARE @id INT
SET @id = 0
UPDATE Satellites SET @id = SatelliteID = @id + 1



ALTER TABLE YourTable DROP COLUMN IDCol