Insert auto increment primary key to existing table

Question

An ALTER TABLE statement adding the PRIMARY KEY column works correctly in my testing:

ALTER TABLE tbl ADD id INT PRIMARY KEY AUTO_INCREMENT;

On a temporary table created for testing purposes, the above statement created the AUTO_INCREMENT id column and inserted auto-increment values for each existing row in the table, starting with 1.

suppose you don't have column for auto increment like id, no, then you can add using following query:

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

If you've column, then alter to auto increment using following query:

 ALTER TABLE table_name MODIFY column_name datatype(length) AUTO_INCREMENT PRIMARY KEY

For those like myself getting a Multiple primary key defined error try:

ALTER TABLE `myTable` ADD COLUMN `id` INT AUTO_INCREMENT UNIQUE FIRST NOT NULL;

On MySQL v5.5.31 this set the id column as the primary key for me and populated each row with an incrementing value.

yes, something like this would do it, might not be the best though, you might wanna make a backup

$get_query = mysql_query("SELECT `any_field` FROM `your_table`");

$auto_increment_id = 1;

while($row = mysql_fetch_assoc($get_query))
{
  $update_query = mysql_query("UPDATE `your_table` SET `auto_increment_id`=$auto_increment_id WHERE `any_field` = '".$row['any_field']."'");
  $auto_increment_id++;
}

notice that the the any_field you select must be the same when updating.

The easiest and quickest I find is this

ALTER TABLE mydb.mytable 
ADD COLUMN mycolumnname INT NOT NULL AUTO_INCREMENT AFTER updated,
ADD UNIQUE INDEX mycolumnname_UNIQUE (mycolumname ASC);

I was able to adapt these instructions take a table with an existing non-increment primary key, and add an incrementing primary key to the table and create a new composite primary key with both the old and new keys as a composite primary key using the following code:

DROP TABLE  IF EXISTS SAKAI_USER_ID_MAP;

CREATE TABLE SAKAI_USER_ID_MAP (
       USER_ID             VARCHAR (99) NOT NULL,
       EID                 VARCHAR (255) NOT NULL,
       PRIMARY KEY (USER_ID)
);

INSERT INTO SAKAI_USER_ID_MAP VALUES ('admin', 'admin');
INSERT INTO SAKAI_USER_ID_MAP VALUES ('postmaster', 'postmaster');

ALTER TABLE  SAKAI_USER_ID_MAP 
  DROP PRIMARY KEY, 
  ADD _USER_ID INT AUTO_INCREMENT NOT NULL FIRST, 
  ADD PRIMARY KEY ( _USER_ID, USER_ID );

When this is done, the _USER_ID field exists and has all number values for the primary key exactly as you would expect. With the "DROP TABLE" at the top, you can run this over and over to experiment with variations.

What I have not been able to get working is the situation where there are incoming FOREIGN KEYs that already point at the USER_ID field. I get this message when I try to do a more complex example with an incoming foreign key from another table.

#1025 - Error on rename of './zap/#sql-da07_6d' to './zap/SAKAI_USER_ID_MAP' (errno: 150)

I am guessing that I need to tear down all foreign keys before doing the ALTER table and then rebuild them afterwards. But for now I wanted to share this solution to a more challenging version of the original question in case others ran into this situation.

In order to make the existing primary key as auto_increment, you may use:

ALTER TABLE table_name MODIFY id INT AUTO_INCREMENT;