Fix: CVR unique constraint - tillad multiple kunder uden CVR nummer

migrations/999_fix_cvr_unique_constraint.sql

@@ -0,0 +1,13 @@
+-- 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';