Alter a MySQL column to be AUTO_INCREMENT

问题

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 |
+--------------------+

回答1:

ALTER TABLE document MODIFY COLUMN document_id INT auto_increment

回答2:

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

回答3:

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;

回答4:

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.

回答5:

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)

回答6:

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.

回答7:

You can do it like this:

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

回答8:

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)

回答9:

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;

回答10:

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;

回答11:

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 ;

回答12:

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;

回答13:

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;

回答14:

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

回答15:

Just like this:

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

回答16:

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;

回答17:

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>

回答18:

ALTER TABLE table_name MODIFY COLUMN id datatype auto_increment;

回答19:

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

标签

sql

mysql

alter-table