-- Migration: Fix CVR Unique Constraint
-- Allow multiple customers without CVR number (NULL or empty string)

-- Drop old unique constraint
ALTER TABLE customers DROP CONSTRAINT IF EXISTS customers_cvr_number_key;

-- Create partial unique index - only enforce uniqueness for non-empty CVR numbers
CREATE UNIQUE INDEX IF NOT EXISTS customers_cvr_number_unique_idx 
ON customers (cvr_number) 
WHERE cvr_number IS NOT NULL AND cvr_number != '';

COMMENT ON INDEX customers_cvr_number_unique_idx IS 
'Ensures CVR numbers are unique, but allows multiple customers without CVR';