[EDIT]transactionRepositoryにカテゴリ別集計を追記しました。

src/main/java/com/example/demo/app/infra/repository/TransactionRepository.java

@@ -22,5 +22,6 @@ public interface TransactionRepository extends JpaRepository<TransactionEntity,
 	@Query("select sum(t.amount) from TransactionEntity t inner join CategoryEntity c on t.categoryId = c.categoryId where (t.userId = :userId and t.transactionDate between :startDate and :endDate) and c.transactionType = 1")
 	public Integer findTotalIncome(LocalDate startDate, LocalDate endDate, Long userId);
 	
-	
+	@Query("select sum(t.amount) from TransactionEntity t where t.userEntity.userId = :userId and t.categoryEntity.categoryId = :categoryId and t.transactionDate between :startDate and :endDate")
+	public Integer findCategoryExpense(LocalDate startDate, LocalDate endDate, Long userId, Long categoryId);
 }