diff --git a/migrations/000.442.sql b/migrations/000.442.sql
new file mode 100644
index 0000000..670bed0
--- /dev/null
+++ b/migrations/000.442.sql
@@ -0,0 +1,76 @@
+-- ============================================================================
+-- Delete unused discount codes older than 2023-01-01 or having invalid dates.
+-- ============================================================================
+DELETE  FROM discount_code_filters
+ WHERE  discount_code_id IN (
+            SELECT  discountid
+              FROM  discount_codes
+             WHERE  (SELECT COUNT(*) FROM order_rows s WHERE s.sub_type = 'discount_code' AND s.data ->> 'code' = code) = 0
+               AND  ("end" < '2023-01-01' OR  start > "end")
+        );
+
+DELETE  FROM discount_codes
+ WHERE  discountid IN (
+            SELECT  discountid
+              FROM  discount_codes dc
+             WHERE  (SELECT COUNT(*) FROM order_rows s WHERE s.sub_type = 'discount_code' AND s.data ->> 'code' = code) = 0
+               AND  ("end" < '2023-01-01' OR start > "end")
+        );
+
+-- ============================================================================
+-- Delete discounts with codes occuring more than once.
+-- Keep the latest inserted.
+-- ============================================================================
+CREATE INDEX IF NOT EXISTS ix_discount_codes_discountid_lower_code ON discount_codes (discountid, LOWER(code));
+
+DELETE  FROM discount_code_filters
+ WHERE  NOT discount_code_id IN (
+            SELECT  discountid
+              FROM  discount_codes dc
+             WHERE  discountid = (
+                        SELECT  MAX(discountid)
+                          FROM  discount_codes dcs
+                         WHERE  LOWER(dc.code) = LOWER(dcs.code)
+                    )
+        );
+
+DELETE  FROM discount_codes
+ WHERE  NOT discountid IN (
+            SELECT  discountid
+              FROM  discount_codes dc
+             WHERE  discountid = (
+                        SELECT  MAX(discountid)
+                          FROM  discount_codes dcs
+                         WHERE  LOWER(dc.code) = LOWER(dcs.code)
+                    )
+        );
+
+DROP INDEX IF EXISTS ix_discount_codes_discountid_lower_code;
+
+-- ============================================================================
+-- Make existing codes lower cased.
+-- ============================================================================
+
+-- Keep existing updated timestamps
+DROP TRIGGER IF EXISTS updated_timestamp ON public.discount_codes;
+
+UPDATE  discount_codes
+   SET  code = LOWER(code);
+
+CREATE TRIGGER updated_timestamp
+    BEFORE UPDATE
+    ON public.discount_codes
+    FOR EACH ROW
+    EXECUTE FUNCTION public.updated_timestamp();
+
+-- ============================================================================
+-- Make code unique.
+-- ============================================================================
+CREATE UNIQUE INDEX IF NOT EXISTS uix_discount_codes_lower_code ON discount_codes (LOWER(code));
+
+-- ============================================================================
+-- Ensure start date is before end date.
+-- ============================================================================
+ALTER TABLE discount_codes
+  ADD CONSTRAINT date_range_check
+CHECK (start <= "end");