DB2中关于rownumber() over()使用问题

以下是错误信息：
ERROR: A WHERE, VALUES, GROUP BY, HAVING, or SET clause includes
an invalid reference, such as a column or OLAP function.
DB2 SQL Error: SQLCODE=-120, SQLSTATE=42903, SQLERRMC=null,
DRIVER=3.69.24 Error Code: -120
DB2 SQL Error: SQLCODE=-727, SQLSTATE=56098,
SQLERRMC=2;-120;42903;, DRIVER=3.69.24
Query = select * from RATE.RISK_CUSTOMER where rownumber() over()
<= 25

group by