Postgres'date_trunc'功能與'在時區'

Question

我想使用date_trunc函數與從列中選擇參數的特定時區。

它的工作原理沒有「在時間區」：

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

它也可以當傳入的參數是一個字符串：

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，當我試圖將兩者結合起來，像這樣：

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

它給了我'交易'或'附近的'語法錯誤''。

我試過用to_char把它轉換成字符串，但沒有運氣。我該如何做這項工作？

Answer 1

如果你想投你created_at field，你必須這樣寫如下：

CAST (transactions.created_at as timestamp) 

因此，最終的查詢應該是這樣的：

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