diff --git a/backend/src/main/resources/db/migration/V9__backfill_user_accounts.sql b/backend/src/main/resources/db/migration/V9__backfill_user_accounts.sql
index 05cee442..ecb020b1 100644
--- a/backend/src/main/resources/db/migration/V9__backfill_user_accounts.sql
+++ b/backend/src/main/resources/db/migration/V9__backfill_user_accounts.sql
@@ -2,10 +2,7 @@ INSERT INTO users (username, password, email, fullName, phone, role, active, tok
 SELECT
     CONCAT('customer_', c.customerId) AS username,
     '$2a$10$mE0D/HrnCuqFeEqMy0NJwuy2jkoRYjQ7GrKcc/7QQ0r2AqnZTvyGq' AS password,
-    CASE
-        WHEN EXISTS (SELECT 1 FROM users u WHERE u.email = c.email) THEN CONCAT('customer_', c.customerId, '@petshop.local')
-        ELSE c.email
-    END AS email,
+    CONCAT('customer_', c.customerId, '@petshop.local') AS email,
     CONCAT(c.firstName, ' ', c.lastName) AS fullName,
     CONCAT('200-000-', LPAD(c.customerId, 4, '0')) AS phone,
     'CUSTOMER' AS role,
@@ -23,10 +20,7 @@ INSERT INTO users (username, password, email, fullName, phone, role, active, tok
 SELECT
     CONCAT('employee_', e.employeeId) AS username,
     '$2a$10$mE0D/HrnCuqFeEqMy0NJwuy2jkoRYjQ7GrKcc/7QQ0r2AqnZTvyGq' AS password,
-    CASE
-        WHEN EXISTS (SELECT 1 FROM users u WHERE u.email = e.email) THEN CONCAT('employee_', e.employeeId, '@petshop.local')
-        ELSE e.email
-    END AS email,
+    CONCAT('employee_', e.employeeId, '@petshop.local') AS email,
     CONCAT(e.firstName, ' ', e.lastName) AS fullName,
     CONCAT('300-000-', LPAD(e.employeeId, 4, '0')) AS phone,
     CASE
@@ -44,13 +38,13 @@ WHERE e.user_id IS NULL
   );
 
 UPDATE customer c
-JOIN users u ON u.email = c.email
+JOIN users u ON u.username = CONCAT('customer_', c.customerId)
    AND u.role = 'CUSTOMER'
 SET c.user_id = u.id
 WHERE c.user_id IS NULL;
 
 UPDATE employee e
-JOIN users u ON u.email = e.email
+JOIN users u ON u.username = CONCAT('employee_', e.employeeId)
    AND u.role IN ('STAFF', 'ADMIN')
 SET e.user_id = u.id
 WHERE e.user_id IS NULL;