diff --git a/backend/src/main/java/com/xly/erp/module/usr/mapper/SysUserMapper.java b/backend/src/main/java/com/xly/erp/module/usr/mapper/SysUserMapper.java
index 60ed176..35d2b11 100644
--- a/backend/src/main/java/com/xly/erp/module/usr/mapper/SysUserMapper.java
+++ b/backend/src/main/java/com/xly/erp/module/usr/mapper/SysUserMapper.java
@@ -42,4 +42,10 @@ public interface SysUserMapper extends BaseMapper<SysUser> {
             "SET iFailedLoginCount = 0, tLockUntil = NULL, tLastLoginDate = NOW() " +
             "WHERE iIncrement = #{userId}")
     int markLoginSuccess(@Param("userId") Integer userId);
+
+    @Select("SELECT EXISTS(SELECT 1 FROM sys_user WHERE sUsername = #{username})")
+    boolean existsByUsername(@Param("username") String username);
+
+    @Select("SELECT EXISTS(SELECT 1 FROM sys_user WHERE sUserCode = #{userCode})")
+    boolean existsByUserCode(@Param("userCode") String userCode);
 }
diff --git a/backend/src/test/java/com/xly/erp/module/usr/mapper/SysUserMapperTest.java b/backend/src/test/java/com/xly/erp/module/usr/mapper/SysUserMapperTest.java
index 76c8cb4..2b11924 100644
--- a/backend/src/test/java/com/xly/erp/module/usr/mapper/SysUserMapperTest.java
+++ b/backend/src/test/java/com/xly/erp/module/usr/mapper/SysUserMapperTest.java
@@ -43,4 +43,24 @@ class SysUserMapperTest {
         SysUser user = userMapper.selectByUsername("nobody");
         assertNull(user);
     }
+
+    @Test
+    void existsByUsername_trueForExisting() {
+        assertTrue(userMapper.existsByUsername(LoginTestSeeder.USER_OK));
+    }
+
+    @Test
+    void existsByUsername_falseForUnknown() {
+        assertFalse(userMapper.existsByUsername("nobody"));
+    }
+
+    @Test
+    void existsByUserCode_trueForExisting() {
+        assertTrue(userMapper.existsByUserCode("U001"));
+    }
+
+    @Test
+    void existsByUserCode_falseForUnknown() {
+        assertFalse(userMapper.existsByUserCode("UXXX"));
+    }
 }