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我有这个 MySQL 查询：

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

Reservations 表可以包含任何给定日历日期的任意数量的记录，或者根本不包含任何记录。CalendarOverrides 表可以正好包含每个日历日期的 1 条或 0 条记录。我正在尝试将结果合并在一起，但并不完全正确。

这是我的结果集：

在此处输入图像描述

预订第 23 天是个问题。我希望将这 2 条记录合并为 1，以便 5 个值是： 23、6、8、1
、[空白/空]

澄清：
- ReservationDay 在两个表中（在 CalendarOverrides 中命名为 CalendarDate）
- SleighSeats 和 CabSeats 存在仅在 Reservations 表中
- IsFullMoon 和 OverrideText 仅存在于 CalendarOverrides 表


中联合中的顶部查询将已经合并同一 ReservationDay 上的所有 Reservations 记录，但是如何将底部查询中的任何记录与顶部查询中的记录合并，为同一个预订日？（因此任何一天的记录都不会超过 1 条。）

4

2 回答 2

2 
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
于 2013-02-21T06:16:49.763 回答
0 
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 支持它，您也应该能够执行完全连接（由于COALESCEwhere 子句，这可能会更慢？）：

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
于 2013-02-21T06:20:55.053 回答