SQL: function trunc(timestamp without time zone, "unknown") 不存在

Question

我正在尝试使用以下代码将日期列转换为星期:

select trunc(join_date, 'D') as join_wk from my_table

但是我得到了以下错误:

function trunc(timestamp without time zone, "unknown") does not exist
  Hint: No function matches the given name and argument types. You may need to add explicit type casts.

其中 join_date 的格式为:

2017-08-24 14:49:59

我在查询中做错了什么？谢谢!

Answer 1

函数的名字是date_trunk，你必须交换参数:

SELECT DATE_TRUNC('D', join_date) AS join_wk FROM my_table