ALTER TABLE paint_primer_sizes ADD COLUMN coverage_m2 NUMERIC NOT NULL DEFAULT 1;

UPDATE paint_primer_sizes SET coverage_m2 = 3.5 WHERE liters = 0.9;
UPDATE paint_primer_sizes SET coverage_m2 = 11 WHERE liters = 2.7;
UPDATE paint_primer_sizes SET coverage_m2 = 2 WHERE liters = 0.5;