Create delayed_order_emails table (#296)

migrations/000.392.sql

@@ -0,0 +1,17 @@
+-- Delayed order emails table
+
+CREATE TYPE delayed_orders_email_type AS ENUM ('automatic', 'manual');
+CREATE TYPE delayed_orders_email_status as ENUM ('created', 'sent', 'error', 'blocked');
+
+CREATE TABLE delayed_orders_email (
+    id SERIAL PRIMARY KEY,
+    order_id int REFERENCES orders (id) NOT NULL,
+    type delayed_orders_email_type NOT NULL,
+    status delayed_orders_email_status NOT NULL,
+    date timestamp with time zone DEFAULT now()
+);
+
+-- This creates a partial unique constraint.
+-- It enforces max one automatic email; allows multiple manual emails; enables blocking automatic email.
+CREATE UNIQUE INDEX unique_automatic_delayed_orders_emails ON delayed_orders_email (order_id) WHERE (type = 'automatic');
+