diff --git a/think-backend.greaterchiangmai.com/app/Http/Controllers/Backend/ArticleController.php b/think-backend.greaterchiangmai.com/app/Http/Controllers/Backend/ArticleController.php
index d683afd..22f5834 100644
--- a/think-backend.greaterchiangmai.com/app/Http/Controllers/Backend/ArticleController.php
+++ b/think-backend.greaterchiangmai.com/app/Http/Controllers/Backend/ArticleController.php
@@ -119,7 +119,7 @@ class ArticleController extends Controller
         // prepared data
         $data = [
             'category_id' => 1,
-            'sub_category_ids' => implode(", ", $sub_categories),
+            'sub_category_ids' => implode(",", $sub_categories),
             'due_date' => $formattedDate,
             'name' => $name,
             'name_en' => $name_en,
@@ -207,7 +207,7 @@ class ArticleController extends Controller
         $formattedDate = $dateObject->format('Y-m-d'); // Convert to YYYY-MM-DD
         $data = [
             'category_id' => 1,
-            'sub_category_ids' => implode(", ", $sub_categories),
+            'sub_category_ids' => implode(",", $sub_categories),
             'due_date' => $formattedDate,
             'active' => $active,
             'name' => $name,
diff --git a/think-backend.greaterchiangmai.com/app/Http/Controllers/Backend/ArticleWhereElseController.php b/think-backend.greaterchiangmai.com/app/Http/Controllers/Backend/ArticleWhereElseController.php
index 0ed44bc..9f855f7 100644
--- a/think-backend.greaterchiangmai.com/app/Http/Controllers/Backend/ArticleWhereElseController.php
+++ b/think-backend.greaterchiangmai.com/app/Http/Controllers/Backend/ArticleWhereElseController.php
@@ -118,7 +118,7 @@ class ArticleWhereElseController extends Controller
         // prepared data
         $data = [
             'category_id' => 2,
-            'sub_category_ids' => implode(", ", $sub_categories),
+            'sub_category_ids' => implode(",", $sub_categories),
             'due_date' => $formattedDate,
             'name' => $name,
             'name_en' => $name_en,
@@ -206,7 +206,7 @@ class ArticleWhereElseController extends Controller
         $formattedDate = $dateObject->format('Y-m-d'); // Convert to YYYY-MM-DD
         $data = [
             'category_id' => 2,
-            'sub_category_ids' => implode(", ", $sub_categories),
+            'sub_category_ids' => implode(",", $sub_categories),
             'due_date' => $formattedDate,
             'active' => $active,
             'name' => $name,
diff --git a/think-backend.greaterchiangmai.com/database/migrations/2026_10_26_000000_normalize_article_sub_category_ids.php b/think-backend.greaterchiangmai.com/database/migrations/2026_10_26_000000_normalize_article_sub_category_ids.php
new file mode 100644
index 0000000..38d536e
--- /dev/null
+++ b/think-backend.greaterchiangmai.com/database/migrations/2026_10_26_000000_normalize_article_sub_category_ids.php
@@ -0,0 +1,22 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Support\Facades\DB;
+
+// Article insert/update used to store sub_category_ids as "15, 21" (comma+space).
+// Every reader uses FIND_IN_SET(?, sub_category_ids), which never matches " 21",
+// so only the first checked sub-category was ever visible. Strip the spaces.
+return new class extends Migration
+{
+    public function up(): void
+    {
+        DB::table('article')
+            ->where('sub_category_ids', 'like', '% %')
+            ->update(['sub_category_ids' => DB::raw("REPLACE(sub_category_ids, ' ', '')")]);
+    }
+
+    public function down(): void
+    {
+        // Irreversible by design: the spaced format was a bug, not a schema.
+    }
+};