合併相關記錄

Question

我有這樣的MySQL查詢：

select day(ReservationDate) as ReservationDay, sum(SleighSeats) as SleighSeats, sum(CabSeats) as CabSeats, 0 as IsFullMoon, '' as OverrideText 
from Reservations 
where month(ReservationDate) = 2 
group by ReservationDate 
union 
select day(CalendarDate) as ReservationDay, 0 as SleighSeats, 0 as CabSeats, IsFullMoon, OverrideText 
from CalendarOverrides 
where month(CalendarDate) = 2 
group by CalendarDate 
order by ReservationDay 

的預訂表可以包含任何給定的日曆日期的任何數量的記錄，或者根本沒有。 CalendarOverrides表可以爲每個日曆日期準確包含1或0個記錄。我試圖將結果合併在一起，但沒有完全正確。

這裏是我的結果集：

預訂23天的問題。我想那些2個記錄在1，從而合併該5倍的值是：
23，6，8，1，[空白/空]

澄清：
- ReservationDay是在兩個表中（名爲CalendarDate在CalendarOverrides）
- SleighSeats和CabSeats只存在於預訂表
- IsFullMoon和OverrideText只有在CalendarOverrides表中存在


在工會已經將合併所有預訂同一ReservationDay記錄的頂部查詢，但我怎樣才能合併底部查詢中的記錄與記錄中的記錄e頂部查詢，對於同一ReservationDay？ （所以有從不爲任何一天超過1分的紀錄。）

Answer 1

select 
    ReservationDay, 
    max(SleighSeats) as SleighSeats, 
    max(CabSeats) as CabSeats, 
    max(IsFullMoon) as IsFullMoon, 
    max(OverrideText) as OverrideText 
from (

    select 
     day(ReservationDate) as ReservationDay, 
     sum(SleighSeats) as SleighSeats, 
     sum(CabSeats) as CabSeats, 
     0 as IsFullMoon, 
     '' as OverrideText 
    from Reservations 
    where month(ReservationDate) = 2 
    group by ReservationDate 
    union 
    select 
     day(CalendarDate) as ReservationDay, 
     0 as SleighSeats, 
     0 as CabSeats, 
     IsFullMoon, 
     OverrideText 
    from CalendarOverrides 
    where month(CalendarDate) = 2 
    group by CalendarDate, IsFullMoon, OverrideText 
) as subtbl 
group by ReservationDay 
order by ReservationDay, IsFullMoon 

Answer 2

select day(ReservationDate) as ReservationDay, sum(SleighSeats) as SleighSeats, 
    sum(CabSeats) as CabSeats, COALESCE(IsFullMoon,0) as IsFullMoon, 
    COALESCE(OverrideText,'') as OverrideText 
from Reservations 
left outer join CalendarOverrides 
    ON Reservations.ReservationDate = CalendarOverrides.CalendarDate 
where month(ReservationDate) = 2 
group by ReservationDate, IsFullMoon, OverrideText 

union all 

select day(CalendarDate) as ReservationDay, 0 as SleighSeats, 
    0 as CabSeats, IsFullMoon, 
    OverrideText 
from CalendarOverrides 
where month(CalendarDate) = 2 
and NOT EXISTS 
(
    SELECT 1 
    FROM Reservations 
    WHERE Reservations.ReservationDate = CalendarOverrides.CalendarDate 
) 

order by ReservationDay 

---

如果您的RDBMS支持的話，你也應該能夠做到這一點會完全加入（這可能因爲where子句中的COALESCE？）：

select day(COALESCE(ReservationDate, CalendarDate)) as ReservationDay, 
    COALESCE(sum(SleighSeats),0) as SleighSeats, 
    COALESCE(sum(CabSeats),0) as CabSeats, COALESCE(IsFullMoon,0) as IsFullMoon, 
    COALESCE(OverrideText,'') as OverrideText 
from Reservations 
full join CalendarOverrides 
    ON Reservations.ReservationDate = CalendarOverrides.CalendarDate 
where month(COALESCE(ReservationDate, CalendarDate)) = 2 
group by ReservationDate, CalendarDate, IsFullMoon, OverrideText 
order by ReservationDay