過濾數據

Question

我有一個像

PERIODID PERIODSTART PERIODEND PRICE STARTDOW 
1  2012-12-01 2012-12-10 10 6 
2  2012-12-11 2012-12-20 20 -1 
3  2012-12-21 2012-12-30 30 -1 

一套時期東西意思就是保留在第1期開始，必須在星期六，而不是週期2和3

如果我從2012-12-10 - 2012-12-15有預訂我想> - 過濾日期爲幾天（不是問題） - 檢查是否保留星期六開始。過濾器應該只用於頂部（或第一行），我不知道如何做到這一點。如果預訂沒有在星期六開始，則不應返回任何行。

我試圖

select * from periods p 
where 
((@ReservationStart between p.periodstart and p.periodend) 
or 
(@ReservationEnd between p.periodstart and p.periodend)) 
and ((select top 1 datepart(weekday, startdow) from periods where p.hotelID = period.hotelID order by period.periodstart) in (@datepart(weekday, @ReservationStart), -1)) 

有沒有辦法做的更好，或者優化代碼對於大數據量的更好嗎？

Answer 1

嗯，不清楚你的意思是第一行。預訂的第一個階段？您是否使用此測試來測試預訂是否在正確的DOW上開始？

set datefirst 1 -- make Monday return 1 when calling datepart(day,...) 

-- if reservation starts on STARTDOW, this will return a single row. 
-- if not, it will return an empty record set 
select top (1) * from periods p 
where @ReservationStart between p.periodstart and p.periodend 
    and p.STARTDOW in (-1, datepart(day,@ReservationStart)) 

編輯

也許這樣的事情呢？

set datefirst 1 -- make Monday return 1 when calling datepart(day,...) 

-- return all periods of the reservation 
-- modify as necessary if you only want the first and last periods, as in your example. 
select * from periods p 
where p.periodend >= @ReservationStart 
    and p.periodstart <= @ReservationEnd 
    -- but only if the start date falls on an allowed DOW 
    and exists (
    select * from periods p2 
    where @ReservationStart between p2.periodstart and p2.periodend 
     and p2.STARTDOW in (-1, datepart(day,@ReservationStart)) 
     and p2.hotelID = p.hotelID -- necessary correlation condition 
    )