我想通过在pgadmin中加入两个表来创建数据透视表视图

Question

我想创建一个数据透视表视图，显示每个travel_mode的预订月份总月份。

表1预订 - 时间戳，预订，PROVIDER_ID 表2提供者 - PROVIDER_ID，TRAVEL_MODE

透视表功能和交叉功能不被用来做此工作。我想要使​​用连接或其他功能。

我不明白这个查询我试图运行的问题，它显示“关系X不存在”

SELECT c.month, train.amount, bus.amount, air.amount 
FROM (SELECT x.month 
     FROM (SELECT to_char(date_,'month') as month, travel_mode, sum(bookings) as amount 
    from bookings as b 
    join providers as p 
    on b.provider_id=p.provider_id 
    group by month, travel_mode) x 
     group by x.month 
    ) c 
JOIN x train ON c.month = train.month AND train.amount = 'train' 
JOIN x bus ON c.month = bus.month AND bus.amount = 'bus' 
JOIN x air ON c.month = air.month AND air.amount = 'air' 
; 

Answer 1

如果我仔细分析查询我认为这是你是什么努力做到：

with x as (
    SELECT to_char(date_,'month') as month, travel_mode, sum(bookings) as amount 
    from bookings as b 
    join providers as p on b.provider_id=p.provider_id 
    group by month, travel_mode) x 
) 
SELECT c.month, train.amount, bus.amount, air.amount 
FROM (
    SELECT x.month 
    FROM x 
    group by x.month 
) c 
    JOIN x train ON c.month = train.month AND train.amount = 'train' 
    JOIN x bus ON c.month = bus.month AND bus.amount = 'bus' 
    JOIN x air ON c.month = air.month AND air.amount = 'air' 

如果你想加入到查询（派生表）的结果多次，你必须将它放入一个common table expression

但select month from x group by month部分对我没有任何意义。