How to add a primary key to a MySQL table?

Question

This is what I tried but it fails:

alter table goods add column `id` int(10) unsigned primary AUTO_INCREMENT;

Does anyone have a tip?

Answer 1

If your table is quite big better not use the statement:

alter table goods add column `id` int(10) unsigned primary KEY AUTO_INCREMENT;

because it makes a copy of all data in a temporary table, alter table and then copies it back. Better do it manually. Rename your table:

rename table goods to goods_old;

create new table with primary key and all necessary indexes:

create table goods (
    id  int(10) unsigned not null AUTO_INCREMENT
    ... other columns ...
    primary key (id)
);

move all data from the old table into new, disabling keys and indexes to speed up copying:

-- USE THIS FOR MyISAM TABLES:

SET UNIQUE_CHECKS=0;
    ALTER TABLE goods DISABLE KEYS;
        INSERT INTO goods (... your column names ...) SELECT ... your column names FROM goods_old; 
    ALTER TABLE goods ENABLE KEYS;
SET UNIQUE_CHECKS=1;

OR

-- USE THIS FOR InnoDB TABLES:

SET AUTOCOMMIT = 0; SET UNIQUE_CHECKS=0; SET FOREIGN_KEY_CHECKS=0;
    INSERT INTO goods (... your column names ...) SELECT ... your column names FROM goods_old; 
SET FOREIGN_KEY_CHECKS=1; SET UNIQUE_CHECKS=1; COMMIT; SET AUTOCOMMIT = 1;

It takes 2 000 seconds to add PK to a table with ~200 mln rows.