Tighten user linking

backend/src/main/resources/db/migration/V9__backfill_user_accounts.sql

@@ -2,7 +2,10 @@ 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,
-    c.email,
+    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(c.firstName, ' ', c.lastName) AS fullName,
     CONCAT('200-000-', LPAD(c.customerId, 4, '0')) AS phone,
     'CUSTOMER' AS role,
@@ -14,14 +17,16 @@ WHERE c.user_id IS NULL
       SELECT 1
       FROM users u
       WHERE u.username = CONCAT('customer_', c.customerId)
-         OR u.email = c.email
   );
 
 INSERT INTO users (username, password, email, fullName, phone, role, active, tokenVersion)
 SELECT
     CONCAT('employee_', e.employeeId) AS username,
     '$2a$10$mE0D/HrnCuqFeEqMy0NJwuy2jkoRYjQ7GrKcc/7QQ0r2AqnZTvyGq' AS password,
-    e.email,
+    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(e.firstName, ' ', e.lastName) AS fullName,
     CONCAT('300-000-', LPAD(e.employeeId, 4, '0')) AS phone,
     CASE
@@ -36,7 +41,6 @@ WHERE e.user_id IS NULL
       SELECT 1
       FROM users u
       WHERE u.username = CONCAT('employee_', e.employeeId)
-         OR u.email = e.email
   );
 
 UPDATE customer c