diff --git a/backend/script/sql/update/aihr_20260718_hotfix_assignments_collation.sql b/backend/script/sql/update/aihr_20260718_hotfix_assignments_collation.sql
new file mode 100644
index 00000000..4f1d29cc
--- /dev/null
+++ b/backend/script/sql/update/aihr_20260718_hotfix_assignments_collation.sql
@@ -0,0 +1,32 @@
+-- Emergency collation alignment for aihr_practice_assignment.
+-- Root cause: production database uses utf8mb4_general_ci for tenant_id column
+-- (inherited from RuoYi base schema), but ext_party_id column lacks explicit
+-- COLLATE clause and inherits utf8mb4_0900_ai_ci from the table DEFAULT.
+-- When the subquery JOIN in AihrPracticeSeedService.assignments() compares
+-- aihr_practice_assignment.ext_party_id = aihr_practice_question_feedback.ext_party_id,
+-- MySQL rejects the implicit collation coercion with error 1267.
+--
+-- Fix: align ext_party_id column collation with the canonical tenant_id collation
+-- already in use by the target database (utf8mb4_general_ci in production).
+
+SET @assignments_target_collation := (
+  SELECT collation_name
+    FROM information_schema.columns
+   WHERE table_schema = DATABASE()
+     AND table_name = 'aihr_practice_assignment'
+     AND column_name = 'tenant_id'
+   LIMIT 1
+);
+SET @assignments_target_collation := COALESCE(@assignments_target_collation, 'utf8mb4_0900_ai_ci');
+
+SET @assignments_ddl := CONCAT(
+  'ALTER TABLE `aihr_practice_assignment` MODIFY COLUMN `ext_party_id` varchar(100) COLLATE ',
+  @assignments_target_collation,
+  ' NOT NULL COMMENT ''员工外部主体或手机号'''
+);
+PREPARE assignments_stmt FROM @assignments_ddl;
+EXECUTE assignments_stmt;
+DEALLOCATE PREPARE assignments_stmt;
+
+SET @assignments_ddl := NULL;
+SET @assignments_target_collation := NULL;