diff --git a/src/exporters/mysql_exporter.py b/src/exporters/mysql_exporter.py
index da8ad25..231c783 100644
--- a/src/exporters/mysql_exporter.py
+++ b/src/exporters/mysql_exporter.py
@@ -171,7 +171,7 @@
 -- =============================================
 CREATE TABLE orders (
 id INT NOT NULL AUTO_INCREMENT,
- order_number VARCHAR(30) NOT NULL UNIQUE,
+ order_number VARCHAR(30) NOT NULL,
 customer_id INT NOT NULL,
 address_id INT NOT NULL,
 staff_id INT NULL,
@@ -188,6 +188,7 @@
 created_at DATETIME NOT NULL,
 updated_at DATETIME NOT NULL,
 PRIMARY KEY (id, ordered_at),
+ UNIQUE KEY uq_order_number (order_number, ordered_at),
 INDEX idx_orders_customer (customer_id),
 INDEX idx_orders_status (status),
 INDEX idx_orders_ordered_at (ordered_at)
diff --git a/src/exporters/postgresql_exporter.py b/src/exporters/postgresql_exporter.py
index 436f770..2e881a7 100644
--- a/src/exporters/postgresql_exporter.py
+++ b/src/exporters/postgresql_exporter.py
@@ -231,7 +231,7 @@
 -- =============================================
 CREATE TABLE orders (
 id INT GENERATED ALWAYS AS IDENTITY,
- order_number VARCHAR(30) NOT NULL UNIQUE,
+ order_number VARCHAR(30) NOT NULL,
 customer_id INT NOT NULL,
 address_id INT NOT NULL,
 staff_id INT NULL,
@@ -247,7 +247,8 @@
 cancelled_at TIMESTAMP NULL,
 created_at TIMESTAMP NOT NULL,
 updated_at TIMESTAMP NOT NULL,
- PRIMARY KEY (id, ordered_at)
+ PRIMARY KEY (id, ordered_at),
+ UNIQUE (order_number, ordered_at)
 ) PARTITION BY RANGE (ordered_at);
 
 CREATE TABLE orders_2015 PARTITION OF orders
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