Postgres＆＃39; date_trunc＆＃39;在时区＆＃39;的功能

Question

我试图将date_trunc函数用于从列中选择参数的特定时区。

没有＆＃39;在时区＆＃39;：

SELECT (date_trunc('day', transactions.created_at))::DATE AS period_start FROM transactions LIMIT 1

当传入的参数是字符串时，它也有效：

SELECT (date_trunc('day', TIMESTAMP '2015-09-04 16:00:00' at time zone '+08:00'))::DATE AS period_start FROM transactions LIMIT 1

但是当我试图将两者结合起来时：

SELECT (date_trunc('day', TIMESTAMP transactions.created_at at time zone '+08:00'))::DATE AS period_start FROM transactions LIMIT 1

它在＆＃34;交易＆＃34;＆＃39;附近或附近给了我一个语法错误。

我尝试使用to_char将其转换为字符串，但也没有运气。我怎样才能做到这一点？

Answer 1

如果您想要投射created_at field，则必须按如下方式编写：

 CAST (transactions.created_at as timestamp)

所以你的最终查询应该是这样的：

SELECT (date_trunc('day', CAST (transactions.created_at as timestamp) at time zone '+08:00'))::DATE AS period_start 
FROM transactions LIMIT 1