CONCATenate columns to a surrogate key

-- Count the number of distinct rows with columns make, model
SELECT COUNT(DISTINCT(make, model)) 
FROM cars;

-- Add the id column
ALTER TABLE cars
ADD COLUMN id varchar(128);

-- Update id with make + model
UPDATE cars
SET id = CONCAT(make, model);

-- Make id a primary key
ALTER TABLE cars
add constraint id_pk primary key(id);

-- Have a look at the table
SELECT * FROM cars;