diff --git a/app/crud.py b/app/crud.py
index ce51659..1279b92 100644
--- a/app/crud.py
+++ b/app/crud.py
@@ -1,11 +1,21 @@
 from sqlalchemy.orm import Session
 from app import models
+from typing import List
 
-def get_customers(db: Session):
+# ---- Customers ----
+def get_customers(db: Session) -> List[models.Customer]:
     return db.query(models.Customer).all()
 
-def get_accounts(db: Session):
-    return db.query(models.Account).all()
+# ---- Accounts ----
+def get_accounts(db: Session, customer_id: int = None) -> List[models.Account]:
+    query = db.query(models.Account)
+    if customer_id is not None:
+        query = query.filter(models.Account.customer_id == customer_id)
+    return query.all()
 
-def get_transactions(db: Session):
-    return db.query(models.Transactions).all()
+# ---- Transactions ----
+def get_transactions(db: Session, account_id: str = None) -> List[models.Transaction]:
+    query = db.query(models.Transaction)
+    if account_id is not None:
+        query = query.filter(models.Transaction.account_id == account_id)
+    return query.all()