diff --git a/backend/src/main/java/com/waa/project/repository/DiscussionCommentsRepository.java b/backend/src/main/java/com/waa/project/repository/DiscussionCommentsRepository.java
index 7dcbc80..28d7946 100644
--- a/backend/src/main/java/com/waa/project/repository/DiscussionCommentsRepository.java
+++ b/backend/src/main/java/com/waa/project/repository/DiscussionCommentsRepository.java
@@ -4,9 +4,12 @@
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.Pageable;
 import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Modifying;
 import org.springframework.data.jpa.repository.Query;
+import org.springframework.data.repository.query.Param;
 import org.springframework.stereotype.Repository;
 
+import java.util.List;
 import java.util.Optional;
 
 @Repository
@@ -23,4 +26,15 @@ public interface DiscussionCommentsRepository extends JpaRepository<DiscussionCo
             nativeQuery = true
     )
     Page<DiscussionComments> findByParentCommentId(Long parentCommentId, Pageable pageable);
-}
+
+    void deleteAllByParentCommentId(DiscussionComments id);
+
+    List<DiscussionComments> findAllByDiscussionId(Long discussionId);
+
+    @Modifying
+    @Query("DELETE FROM DiscussionComments dc WHERE dc.parentCommentId.id IN :parentCommentIds")
+    void deleteAllByParentCommentIds(@Param("parentCommentIds") List<Long> parentCommentIds);
+
+    void deleteByDiscussionId(Long discussionId);
+
+}
\ No newline at end of file
diff --git a/backend/src/main/java/com/waa/project/service/DiscussionCommentsService.java b/backend/src/main/java/com/waa/project/service/DiscussionCommentsService.java
index a437a0c..6c36e0f 100644
--- a/backend/src/main/java/com/waa/project/service/DiscussionCommentsService.java
+++ b/backend/src/main/java/com/waa/project/service/DiscussionCommentsService.java
@@ -1,6 +1,7 @@
 package com.waa.project.service;
 
 import com.waa.project.dto.DiscussionCommentsDto;
+import com.waa.project.entity.Discussion;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.Pageable;
 import org.springframework.security.core.userdetails.User;
@@ -16,4 +17,6 @@ public interface DiscussionCommentsService {
     DiscussionCommentsDto updateDiscussionComments(long id, DiscussionCommentsDto commentsDto, User user);
 
     DiscussionCommentsDto deleteDiscussionComments(long id, User user);
-}
+
+    void deleteAllCommentsByDiscussionId(Discussion discussion);
+}
\ No newline at end of file
diff --git a/backend/src/main/java/com/waa/project/service/SubCommentService.java b/backend/src/main/java/com/waa/project/service/SubCommentService.java
index 58aab85..ea0edd3 100644
--- a/backend/src/main/java/com/waa/project/service/SubCommentService.java
+++ b/backend/src/main/java/com/waa/project/service/SubCommentService.java
@@ -14,4 +14,4 @@ public interface SubCommentService {
     DiscussionCommentsDto updateSubDiscussionComments(long id, DiscussionCommentsDto commentsDto, User user);
 
     DiscussionCommentsDto deleteSubDiscussionComments(long id, User user);
-}
+}
\ No newline at end of file
diff --git a/backend/src/main/java/com/waa/project/service/impl/DiscussionCommentsServiceImpl.java b/backend/src/main/java/com/waa/project/service/impl/DiscussionCommentsServiceImpl.java
index f55cd1b..faba2ab 100644
--- a/backend/src/main/java/com/waa/project/service/impl/DiscussionCommentsServiceImpl.java
+++ b/backend/src/main/java/com/waa/project/service/impl/DiscussionCommentsServiceImpl.java
@@ -108,4 +108,4 @@ private Long getUserId(User user) {
         AuthUserResponse userData = userService.findByUsername(user.getUsername());
         return userData.getId();
     }
-}
+}
\ No newline at end of file