renren-fast sql语句

Preparing: SELECT id,null AS 员工号,null AS 员工姓名,null AS 员工职务,null AS 基本工资,null AS 入职日期,null AS 部门编号 FROM emp LIMIT ?,? Parameters: 0(Long), 10(Long) sql语句是怎么生成的，为什么会加null AS？