新增 NOT LIKE、IS NULL 和 IS NOT NULL 操作符，并更新文档示例

README.md

@@ -7,7 +7,7 @@
 - **WHERE**: 条件过滤
 - **ORDER BY**: 排序
 - **LIMIT**: 限制结果数量
-- **操作符**: `=`, `!=`, `>`, `<`, `>=`, `<=`, `IN`, `CONTAINS`, `LIKE`
+- **操作符**: `=`, `!=`, `>`, `<`, `>=`, `<=`, `IN`, `CONTAINS`, `LIKE`, `NOT LIKE`, `IS NULL`, `IS NOT NULL`
 - **逻辑**: `AND`, `OR`
 
 ## 语法示例
@@ -32,6 +32,15 @@ filter(users, "WHERE metadata.region IN ['beijing', 'shanghai']");
 filter(products, "WHERE name LIKE '%Apple%'");
 filter(products, "WHERE name LIKE 'Apple%'");
 filter(products, "WHERE name LIKE '%Phone'");
+
+// NOT LIKE 操作 (排除匹配模式的项)
+filter(products, "WHERE name NOT LIKE '%Apple%'");
+
+// IS NULL 操作 (匹配 null 或 undefined 的值)
+filter(users, "WHERE email IS NULL");
+
+// IS NOT NULL 操作 (匹配非 null 且非 undefined 的值)
+filter(users, "WHERE email IS NOT NULL");
 ```
 
 ## 使用方法
@@ -72,3 +81,32 @@ const premiumUsers = filter(users, "WHERE metadata.tags CONTAINS 'premium'");
 // 查找北京的用户，按创建时间倒序
 const beijingUsers = filter(users, "WHERE metadata.region = 'beijing' ORDER BY metadata.created_at DESC");
 ```
+
+## 新增操作符说明
+
+### NOT LIKE
+排除匹配指定模式的数据项。
+
+```javascript
+// 查找不包含 "Apple" 的产品
+const nonAppleProducts = filter(products, "WHERE name NOT LIKE '%Apple%'");
+```
+
+### IS NULL / IS NOT NULL
+检查字段值是否为 `null` 或 `undefined`。
+
+```javascript
+const usersWithNullEmail = [
+  { name: 'Alice', email: 'alice@example.com', age: 25 },
+  { name: 'Bob', email: null, age: 30 },
+  { name: 'Charlie', email: undefined, age: 35 },
+];
+
+// 查找 email 为 null 或 undefined 的用户
+const usersWithoutEmail = filter(usersWithNullEmail, "WHERE email IS NULL");
+
+// 查找 email 不为 null 且不为 undefined 的用户  
+const usersWithEmail = filter(usersWithNullEmail, "WHERE email IS NOT NULL");
+```
+
+**注意**: `IS NULL` 和 `IS NOT NULL` 会同时检查 JavaScript 的 `null` 和 `undefined` 值。