Alter a MySQL column to be AUTO_INCREMENT

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()          |
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| 5.0.75-0ubuntu10.2 |
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ALTER TABLE document MODIFY COLUMN document_id INT auto_increment

Roland Bouman

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

Rabia Naz khan

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;

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;

You can find more information in the MySQL documentation: http://dev.mysql.com/doc/refman/5.1/en/alter-table.html for the modify column syntax and http://dev.mysql.com/doc/refman/5.1/en/create-table.html for more information about specifying columns.

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)

Håvard S

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.

Aditya Kumar

You can do it like this:

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

KKK

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)

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;

user5082888

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;

Susie

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 ;

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;

Usman Yaqoob

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;

Aminur Rahman

alter table tbl_user MODIFY COLUMN id int(10) auto_increment;

Just like this:

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

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;

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>

ALTER TABLE table_name MODIFY COLUMN id datatype auto_increment;

Doug Cobain

Use the following queries:

ALTER TABLE YourTable DROP COLUMN IDCol

ALTER TABLE YourTable ADD IDCol INT IDENTITY(1,1)

来源：https://stackoverflow.com/questions/2169080/alter-a-mysql-column-to-be-auto-increment

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