PostgreSql round（）给出错误

Question

我有这个查询

SELECT COALESCE(ROUND(discount_rate * 0.1, 2), '0') AS discount_amount,
COALESCE(discount_rate, 0) AS discount_rate 
FROM discount_rate 

并且在执行我的应用程序代码时给出了以下错误，但它在SQLManagerLite查询面板上正常工作。

Error Code (80007) ERROR: function round(double precision, integer) does not exist
  Hint: No function matches the given name and argument types. You might need to add explicit type casts.