如何向现有列添加 AUTO_INCREMENT？

I think you want to MODIFY the column as described for the ALTER TABLE command. It might be something like this:

ALTER TABLE users MODIFY id INTEGER NOT NULL AUTO_INCREMENT;

Before running above ensure that id column has a Primary index.

Alter table table_name modify column_name datatype(length) AUTO_INCREMENT PRIMARY KEY

You should add primary key to auto increment, otherwise you got error in mysql.

This worked for me in case you want to change the AUTO_INCREMENT-attribute for a not-empty-table:

1.)Exported the whole table as .sql file
2.)Deleted the table after export
2.)Did needed change in CREATE_TABLE command
3.)Executed the CREATE_TABLE and INSERT_INTO commands from the .sql-file
...et viola

Simply just add auto_increment Constraint In column or MODIFY COLUMN :-

 ALTER TABLE `emp` MODIFY COLUMN `id` INT NOT NULL UNIQUE AUTO_INCREMENT FIRST;

Or add a column first then change column as -

1. Alter TABLE `emp` ADD COLUMN `id`;


2. ALTER TABLE `emp` CHANGE COLUMN `id` `Emp_id` INT NOT NULL UNIQUE AUTO_INCREMENT FIRST;

Method to add AUTO_INCREMENT to a table with data while avoiding “Duplicate entry” error:

1. Make a copy of the table with the data using INSERT SELECT:

   CREATE TABLE backupTable LIKE originalTable;
   INSERT backupTable SELECT * FROM originalTable;
   

2. Delete data from originalTable (to remove duplicate entries):

   TRUNCATE TABLE originalTable;
   

3. To add AUTO_INCREMENT and PRIMARY KEY

   ALTER TABLE originalTable ADD id INT PRIMARY KEY AUTO_INCREMENT;
   

4. Copy data back to originalTable (do not include the newly created column (id), since it will be automatically populated)

   INSERT originalTable (col1, col2, col3)
   SELECT col1, col2,col3
   FROM backupTable;
   

5. Delete backupTable:

   DROP TABLE backupTable;
   

More on the duplication of tables using CREATE LIKE:

Duplicating a MySQL table, indices, and data

I managed to do this with the following code:

ALTER TABLE `table_name`
CHANGE COLUMN `colum_name` `colum_name` INT(11) NOT NULL AUTO_INCREMENT FIRST;

This is the only way I could make a column auto increment.

INT(11) shows that the maximum int length is 11, you can skip it if you want.

Alter table table_name modify table_name.column_name data_type AUTO_INCREMENT;

eg:

Alter table avion modify avion.av int AUTO_INCREMENT;

ALTER TABLE Table name ADD column datatype AUTO_INCREMENT,ADD primary key(column);

if you have FK constraints and you don't want to remove the constraint from the table. use "index" instead of primary. then you will be able to alter it's type to auto increment

I had existing data in the first column and they were 0's. First I made the first column nullable. Then I set the data for the column to null. Then I set the column as an index. Then I made it a primary key with auto incrementing turned on. This is where I used another persons answer above:

ALTER TABLE `table_name` CHANGE COLUMN `colum_name` `colum_name` INT(11) NOT NULL AUTO_INCREMENT FIRST;

This Added numbers to all the rows of this table starting at one. If I ran the above code first it wasn't working because all the values were 0's. And making it an index was also required before making it auto incrementing. Next I made the column a primary key.

This worked in my case , if you want to change the column attribute to auto-increment which is already having some data

1.GO to structure, select the column to want to change. 2.After selecting the column , choose primary key from the options below. [1]: https://i.stack.imgur.com/r7w8f.png 3.Then change the column attribute to auto-increment using alter method

This is to alter the column adding PRIMARY key:

ALTER TABLE `schema_name`.`table_name`
CHANGE COLUMN `id` `id` INT(11) NOT NULL AUTO_INCREMENT ,
ADD UNIQUE INDEX `id_UNIQUE` (`id` ASC) VISIBLE,
ADD PRIMARY KEY (`id`);

I copied it from MySQL Workbench... I got curious to see if it was possible to do it all in one command. I'm a little rusty in SQL.

If you are working in an specific schema, you don't need to specify it.

The above statement will create the index, set the column as the PRIMARY KEY as well with just one query.

KEEP IN MIND: There could not be duplicated values in the same column, if there are, the statement will fail to commit.