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使用 MySQL 查询 ```sql SELECT created_at FROM users WHERE username = 'your_username'; ``` 使用 Python（MySQLdb）查询 ```python import MySQLdb db = MySQLdb.connect("host", "username", "password", "database") cursor = db.cursor() cursor.execute("SELECT created_at FROM users WHERE username = %s", ('your_username',)) result = cursor.fetchone() print(result[0]) cursor.close() db.close() ``` 使用 PHP（mysqli）查询 ```php $mysqli = new mysqli("host", "username", "password", "database"); $stmt = $mysqli->prepare("SELECT created_at FROM users WHERE username = ?"); $stmt->bind_param("s", $username); $username = 'your_username'; $stmt->execute(); $stmt->bind_result($created_at); $stmt->fetch(); echo $created_at; $stmt->close(); $mysqli->close(); ?> ``` 注意： 确保用你的实际用户名替换 `your_username`。 对于其他编程语言，请参考相应的数据库连接库的文档以获得具体查询方法。