設定時間戳的時間部分爲固定值

Question

我有一個名爲request_date一個TIMESTAMP列的表。

我要選擇此列的值，但有以下條件：如果時間是19:00:00以後，那麼我應該選擇在次日08:00:00（當然，如果時間是08:00:00之前，我應該選擇那天的08:00:00）。

怎麼會是這樣SELECT子句中實現？

Answer 1

SELECT CASE WHEN request_date < TRUNC(request_date) + INTERVAL '8' HOUR 
      THEN TRUNC(request_date) + INTERVAL '8' HOUR 
      WHEN request_date >= TRUNC(request_date) + INTERVAL '19' HOUR 
      THEN TRUNC(request_date) + INTERVAL '32' HOUR 
      ELSE request_date 
      END AS adjusted_request_date 
FROM table_name 

或

SELECT CASE WHEN EXTRACT(HOUR FROM request_date) < 8 
      THEN TRUNC(request_date) + INTERVAL '8' HOUR 
      WHEN EXTRACT(HOUR FROM request_date) >= 19 
      THEN TRUNC(request_date) + INTERVAL '32' HOUR 
      ELSE request_date 
      END AS adjusted_request_date 
FROM table_name 

Answer 2

select 
    case 
     when to_char(request_date,'HH24') >= 19 
     then to_timestamp(to_char(trunc(request_date) +1,'YYYYMMDD') || '0800','YYYYMMDDHH24MI') 
     when to_char(request_date,'HH24') < 8 
     then to_timestamp(to_char(trunc(request_date),'YYYYMMDD') || '0800','YYYYMMDDHH24MI') 
     else request_date 
    end as ReqStartTS