How to Add a Primary Key in MySQL
Last updated July 25, 2026 · By the SaturnSQL team
Use ALTER TABLE ... ADD PRIMARY KEY (columns). To give a keyless table an auto-incrementing id, add the column and the key in one statement. InnoDB rebuilds the table, so expect it to take time on large tables.
ALTER TABLE events ADD PRIMARY KEY (id);Add an AUTO_INCREMENT id
ALTER TABLE events
ADD COLUMN id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY FIRST;The ALTER fails with a duplicate-entry error if the chosen columns contain duplicates; find and remove them first.
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