diff --git a/backend/.sqlx/query-4e022312b61c557d23f4541961f07b7afa8bf1f62f4a8e248d6520864b126a6a.json b/backend/.sqlx/query-4e022312b61c557d23f4541961f07b7afa8bf1f62f4a8e248d6520864b126a6a.json
new file mode 100644
index 0000000..30d2f58
--- /dev/null
+++ b/backend/.sqlx/query-4e022312b61c557d23f4541961f07b7afa8bf1f62f4a8e248d6520864b126a6a.json
@@ -0,0 +1,22 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "\n            SELECT id\n            FROM post\n            WHERE semantic_id = $1 AND deleted_time IS NULL\n            ",
+  "describe": {
+    "columns": [
+      {
+        "ordinal": 0,
+        "name": "id",
+        "type_info": "Int4"
+      }
+    ],
+    "parameters": {
+      "Left": [
+        "Text"
+      ]
+    },
+    "nullable": [
+      false
+    ]
+  },
+  "hash": "4e022312b61c557d23f4541961f07b7afa8bf1f62f4a8e248d6520864b126a6a"
+}
diff --git a/backend/.sqlx/query-f0c2c0fe0a30790e88449da79c859d4e3829b9b2a6a496c9a429a05fbdb2e30a.json b/backend/.sqlx/query-82c4c8d03298009e776d42ae6069182cc318e0b1d8497a675cf4449adcaf1927.json
similarity index 50%
rename from backend/.sqlx/query-f0c2c0fe0a30790e88449da79c859d4e3829b9b2a6a496c9a429a05fbdb2e30a.json
rename to backend/.sqlx/query-82c4c8d03298009e776d42ae6069182cc318e0b1d8497a675cf4449adcaf1927.json
index 7d34ac9..4680dea 100644
--- a/backend/.sqlx/query-f0c2c0fe0a30790e88449da79c859d4e3829b9b2a6a496c9a429a05fbdb2e30a.json
+++ b/backend/.sqlx/query-82c4c8d03298009e776d42ae6069182cc318e0b1d8497a675cf4449adcaf1927.json
@@ -1,6 +1,6 @@
 {
   "db_name": "PostgreSQL",
-  "query": "\n            INSERT INTO post (\n                title, description, preview_image_url, content, published_time\n            ) VALUES ($1, $2, $3, $4, $5)\n            RETURNING id\n            ",
+  "query": "\n            INSERT INTO post (\n                semantic_id, title, description, preview_image_url, content, published_time\n            ) VALUES ($1, $2, $3, $4, $5, $6)\n            RETURNING id\n            ",
   "describe": {
     "columns": [
       {
@@ -11,6 +11,7 @@
     ],
     "parameters": {
       "Left": [
+        "Varchar",
         "Text",
         "Text",
         "Text",
@@ -22,5 +23,5 @@
       false
     ]
   },
-  "hash": "f0c2c0fe0a30790e88449da79c859d4e3829b9b2a6a496c9a429a05fbdb2e30a"
+  "hash": "82c4c8d03298009e776d42ae6069182cc318e0b1d8497a675cf4449adcaf1927"
 }
diff --git a/backend/.sqlx/query-9e486528becb873ace62656c78805034ddca950db7306ee04257d6b589b5a0d9.json b/backend/.sqlx/query-9e486528becb873ace62656c78805034ddca950db7306ee04257d6b589b5a0d9.json
new file mode 100644
index 0000000..bcb449f
--- /dev/null
+++ b/backend/.sqlx/query-9e486528becb873ace62656c78805034ddca950db7306ee04257d6b589b5a0d9.json
@@ -0,0 +1,20 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "\n            UPDATE post\n            SET \n                semantic_id = $1,\n                title = $2, \n                description = $3, \n                preview_image_url = $4, \n                content = $5, \n                published_time = $6\n            WHERE id = $7\n            ",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": [
+        "Varchar",
+        "Text",
+        "Text",
+        "Text",
+        "Text",
+        "Timestamp",
+        "Int4"
+      ]
+    },
+    "nullable": []
+  },
+  "hash": "9e486528becb873ace62656c78805034ddca950db7306ee04257d6b589b5a0d9"
+}
diff --git a/backend/.sqlx/query-d0867ba2857fedcdc9a754d0394c4f040d559118d0b9f8b6f4dcd6e6fde5d381.json b/backend/.sqlx/query-d0867ba2857fedcdc9a754d0394c4f040d559118d0b9f8b6f4dcd6e6fde5d381.json
deleted file mode 100644
index f194863..0000000
--- a/backend/.sqlx/query-d0867ba2857fedcdc9a754d0394c4f040d559118d0b9f8b6f4dcd6e6fde5d381.json
+++ /dev/null
@@ -1,19 +0,0 @@
-{
-  "db_name": "PostgreSQL",
-  "query": "\n            UPDATE post\n            SET \n                title = $1, \n                description = $2, \n                preview_image_url = $3, \n                content = $4, \n                published_time = $5\n            WHERE id = $6\n            ",
-  "describe": {
-    "columns": [],
-    "parameters": {
-      "Left": [
-        "Text",
-        "Text",
-        "Text",
-        "Text",
-        "Timestamp",
-        "Int4"
-      ]
-    },
-    "nullable": []
-  },
-  "hash": "d0867ba2857fedcdc9a754d0394c4f040d559118d0b9f8b6f4dcd6e6fde5d381"
-}
diff --git a/backend/feature/post/src/application/error/post_error.rs b/backend/feature/post/src/application/error/post_error.rs
index 4d13e4e..275efcc 100644
--- a/backend/feature/post/src/application/error/post_error.rs
+++ b/backend/feature/post/src/application/error/post_error.rs
@@ -5,6 +5,8 @@ pub enum PostError {
     NotFound,
     Unauthorized,
     InvalidSemanticId,
+    DuplicatedSemanticId,
+    DuplicatedLabelName,
     Unexpected(anyhow::Error),
 }
 
@@ -17,6 +19,8 @@ impl Display for PostError {
                 f,
                 "Semantic ID shouldn't be numeric and must conform to `^[0-9a-zA-Z_\\-]+$`"
             ),
+            PostError::DuplicatedSemanticId => write!(f, "Semantic ID already exists"),
+            PostError::DuplicatedLabelName => write!(f, "Label name already exists"),
             PostError::Unexpected(e) => write!(f, "Unexpected error: {}", e),
         }
     }
diff --git a/backend/feature/post/src/framework/db/label_db_service_impl.rs b/backend/feature/post/src/framework/db/label_db_service_impl.rs
index f189fd1..9a0d775 100644
--- a/backend/feature/post/src/framework/db/label_db_service_impl.rs
+++ b/backend/feature/post/src/framework/db/label_db_service_impl.rs
@@ -32,7 +32,14 @@ impl LabelDbService for LabelDbServiceImpl {
         )
         .fetch_one(&self.db_pool)
         .await
-        .map_err(|e| PostError::Unexpected(DatabaseError(e).into()))?;
+        .map_err(|e| {
+            if let sqlx::Error::Database(db_err) = &e {
+                if db_err.constraint() == Some("idx_label_name") {
+                    return PostError::DuplicatedLabelName;
+                }
+            }
+            PostError::Unexpected(DatabaseError(e).into())
+        })?;
 
         Ok(id)
     }
@@ -50,7 +57,14 @@ impl LabelDbService for LabelDbServiceImpl {
         )
         .execute(&self.db_pool)
         .await
-        .map_err(|e| PostError::Unexpected(DatabaseError(e).into()))?
+        .map_err(|e| {
+            if let sqlx::Error::Database(db_err) = &e {
+                if db_err.constraint() == Some("idx_label_name") {
+                    return PostError::DuplicatedLabelName;
+                }
+            }
+            PostError::Unexpected(DatabaseError(e).into())
+        })?
         .rows_affected();
 
         if affected_rows == 0 {
diff --git a/backend/feature/post/src/framework/db/post_db_service_impl.rs b/backend/feature/post/src/framework/db/post_db_service_impl.rs
index fa46e0e..ac68214 100644
--- a/backend/feature/post/src/framework/db/post_db_service_impl.rs
+++ b/backend/feature/post/src/framework/db/post_db_service_impl.rs
@@ -211,7 +211,14 @@ impl PostDbService for PostDbServiceImpl {
         )
         .fetch_one(&mut *tx)
         .await
-        .map_err(|e| PostError::Unexpected(DatabaseError(e).into()))?;
+        .map_err(|e| {
+            if let sqlx::Error::Database(db_err) = &e {
+                if db_err.constraint() == Some("idx_post_semantic_id") {
+                    return PostError::DuplicatedSemanticId;
+                }
+            }
+            PostError::Unexpected(DatabaseError(e).into())
+        })?;
 
         for (order, &label_id) in label_ids.iter().enumerate() {
             sqlx::query!(
@@ -266,7 +273,14 @@ impl PostDbService for PostDbServiceImpl {
         )
         .execute(&mut *tx)
         .await
-        .map_err(|e| PostError::Unexpected(DatabaseError(e).into()))?
+        .map_err(|e| {
+            if let sqlx::Error::Database(db_err) = &e {
+                if db_err.constraint() == Some("idx_post_semantic_id") {
+                    return PostError::DuplicatedSemanticId;
+                }
+            }
+            PostError::Unexpected(DatabaseError(e).into())
+        })?
         .rows_affected();
 
         if affected_rows == 0 {
diff --git a/backend/feature/post/src/framework/web/create_label_handler.rs b/backend/feature/post/src/framework/web/create_label_handler.rs
index a06f2c2..ca1fda6 100644
--- a/backend/feature/post/src/framework/web/create_label_handler.rs
+++ b/backend/feature/post/src/framework/web/create_label_handler.rs
@@ -34,7 +34,10 @@ pub async fn create_label_handler(
         Ok(label) => HttpResponse::Created().json(label),
         Err(e) => match e {
             PostError::Unauthorized => HttpResponse::Unauthorized().finish(),
-            PostError::NotFound | PostError::InvalidSemanticId => {
+            PostError::DuplicatedLabelName => HttpResponse::Conflict().finish(),
+            PostError::NotFound
+            | PostError::InvalidSemanticId
+            | PostError::DuplicatedSemanticId => {
                 capture_anyhow(&anyhow!(e));
                 HttpResponse::InternalServerError().finish()
             }
diff --git a/backend/feature/post/src/framework/web/create_post_handler.rs b/backend/feature/post/src/framework/web/create_post_handler.rs
index f8ee1b3..e884022 100644
--- a/backend/feature/post/src/framework/web/create_post_handler.rs
+++ b/backend/feature/post/src/framework/web/create_post_handler.rs
@@ -37,7 +37,8 @@ pub async fn create_post_handler(
         Err(e) => match e {
             PostError::Unauthorized => HttpResponse::Unauthorized().finish(),
             PostError::InvalidSemanticId => HttpResponse::BadRequest().finish(),
-            PostError::NotFound => {
+            PostError::DuplicatedSemanticId => HttpResponse::Conflict().finish(),
+            PostError::NotFound | PostError::DuplicatedLabelName => {
                 capture_anyhow(&anyhow!(e));
                 HttpResponse::InternalServerError().finish()
             }
diff --git a/backend/feature/post/src/framework/web/get_all_labels_handler.rs b/backend/feature/post/src/framework/web/get_all_labels_handler.rs
index 2aac104..7ad0cda 100644
--- a/backend/feature/post/src/framework/web/get_all_labels_handler.rs
+++ b/backend/feature/post/src/framework/web/get_all_labels_handler.rs
@@ -24,7 +24,11 @@ pub async fn get_all_labels_handler(
     match result {
         Ok(labels) => HttpResponse::Ok().json(labels),
         Err(e) => match e {
-            PostError::NotFound | PostError::Unauthorized | PostError::InvalidSemanticId => {
+            PostError::NotFound
+            | PostError::Unauthorized
+            | PostError::InvalidSemanticId
+            | PostError::DuplicatedSemanticId
+            | PostError::DuplicatedLabelName => {
                 capture_anyhow(&anyhow!(e));
                 HttpResponse::InternalServerError().finish()
             }
diff --git a/backend/feature/post/src/framework/web/get_all_post_info_handler.rs b/backend/feature/post/src/framework/web/get_all_post_info_handler.rs
index a18e412..f3f084d 100644
--- a/backend/feature/post/src/framework/web/get_all_post_info_handler.rs
+++ b/backend/feature/post/src/framework/web/get_all_post_info_handler.rs
@@ -36,7 +36,11 @@ pub async fn get_all_post_info_handler(
     match result {
         Ok(post_info_list) => HttpResponse::Ok().json(post_info_list),
         Err(e) => match e {
-            PostError::NotFound | PostError::Unauthorized | PostError::InvalidSemanticId => {
+            PostError::NotFound
+            | PostError::Unauthorized
+            | PostError::InvalidSemanticId
+            | PostError::DuplicatedSemanticId
+            | PostError::DuplicatedLabelName => {
                 capture_anyhow(&anyhow!(e));
                 HttpResponse::InternalServerError().finish()
             }
diff --git a/backend/feature/post/src/framework/web/get_post_by_id_handler.rs b/backend/feature/post/src/framework/web/get_post_by_id_handler.rs
index 891265d..9705eb2 100644
--- a/backend/feature/post/src/framework/web/get_post_by_id_handler.rs
+++ b/backend/feature/post/src/framework/web/get_post_by_id_handler.rs
@@ -34,7 +34,9 @@ pub async fn get_post_by_id_handler(
         Err(e) => match e {
             PostError::NotFound => HttpResponse::NotFound().finish(),
             PostError::Unauthorized => HttpResponse::Unauthorized().finish(),
-            PostError::InvalidSemanticId => {
+            PostError::InvalidSemanticId
+            | PostError::DuplicatedSemanticId
+            | PostError::DuplicatedLabelName => {
                 capture_anyhow(&anyhow!(e));
                 HttpResponse::InternalServerError().finish()
             }
diff --git a/backend/feature/post/src/framework/web/update_label_handler.rs b/backend/feature/post/src/framework/web/update_label_handler.rs
index cb06770..f72352f 100644
--- a/backend/feature/post/src/framework/web/update_label_handler.rs
+++ b/backend/feature/post/src/framework/web/update_label_handler.rs
@@ -40,7 +40,8 @@ pub async fn update_label_handler(
         Err(e) => match e {
             PostError::NotFound => HttpResponse::NotFound().finish(),
             PostError::Unauthorized => HttpResponse::Unauthorized().finish(),
-            PostError::InvalidSemanticId => {
+            PostError::DuplicatedLabelName => HttpResponse::Conflict().finish(),
+            PostError::InvalidSemanticId | PostError::DuplicatedSemanticId => {
                 capture_anyhow(&anyhow!(e));
                 HttpResponse::InternalServerError().finish()
             }
diff --git a/backend/feature/post/src/framework/web/update_post_handler.rs b/backend/feature/post/src/framework/web/update_post_handler.rs
index 40cce3e..ef256b3 100644
--- a/backend/feature/post/src/framework/web/update_post_handler.rs
+++ b/backend/feature/post/src/framework/web/update_post_handler.rs
@@ -1,4 +1,5 @@
 use actix_web::{HttpResponse, Responder, web};
+use anyhow::anyhow;
 use auth::framework::web::auth_middleware::UserId;
 use sentry::integrations::anyhow::capture_anyhow;
 
@@ -39,7 +40,12 @@ pub async fn update_post_handler(
         Err(e) => match e {
             PostError::NotFound => HttpResponse::NotFound().finish(),
             PostError::Unauthorized => HttpResponse::Unauthorized().finish(),
+            PostError::DuplicatedSemanticId => HttpResponse::Conflict().finish(),
             PostError::InvalidSemanticId => HttpResponse::BadRequest().finish(),
+            PostError::DuplicatedLabelName => {
+                capture_anyhow(&anyhow!(e));
+                HttpResponse::InternalServerError().finish()
+            }
             PostError::Unexpected(e) => {
                 capture_anyhow(&e);
                 HttpResponse::InternalServerError().finish()
diff --git a/backend/migrations/20251012123809_add_unique_index_to_label_name.down.sql b/backend/migrations/20251012123809_add_unique_index_to_label_name.down.sql
new file mode 100644
index 0000000..70eca82
--- /dev/null
+++ b/backend/migrations/20251012123809_add_unique_index_to_label_name.down.sql
@@ -0,0 +1,2 @@
+-- Remove unique index from label name column
+DROP INDEX IF EXISTS "idx_label_name";
diff --git a/backend/migrations/20251012123809_add_unique_index_to_label_name.sql b/backend/migrations/20251012123809_add_unique_index_to_label_name.sql
new file mode 100644
index 0000000..4d561ea
--- /dev/null
+++ b/backend/migrations/20251012123809_add_unique_index_to_label_name.sql
@@ -0,0 +1,2 @@
+-- Add unique index to label name column
+CREATE UNIQUE INDEX "idx_label_name" ON "label" ("name");