外部联接-Oracle

Question

我有2个表格

Current Ecpense table
-----------------------

Month-----Type-------spent
Feb 12  Shopping   100 
Feb 12  Food       200
Jan 12  Shopping   456  
Jan 12  Food       452
Jan 12  Fuel       120
Jan 12  Rent       900

Previous Expense
-----------------------
Type------ spent 
Shopping   100
Food       100
Fuel       100
Rent       100

现在我想加入这两个表，预期结果是：

Month-----Type-------spent-----Previous Spent
Feb 12  Shopping   100      100
Feb 12  Food       200      100
Feb 12  Fuel       0        100
Feb 12  Rent       0        100
Jan 12  Shopping   456      100
Jan 12  Food       452      100
Jan 12  Fuel       120      100
Jan 12  Rent       900      100

有没有办法做到这一点？

Answer 1

尝试：

select m.month,
       p.type,
       coalesce(c.spent,0) spent,
       p.spent previous_spent
from (select distinct month from current_expense) m
cross join previous_expense p
left join current_expense c 
       on m.month = c.month and p.type = c.type

Answer 2

通用Oracle语法

从current_expense a，previous_expense b中选择a。*，b。花费'previous Sent'，其中a.type = b.type

或标准中的同一件事

从current_expense中选择a。*，b.spent'previous Sent'作为内部联接，previous_expense作为a.type = b.type上的b

Answer 3

我倾向于用SQL92写（更多的SQLness和更少的Oracle-ness）
这是我的答案：

select
    z.month        as month          ,
    z.type         as type           ,
    nvl(c.spent,0) as spent          ,
    nvl(p.spent,0) as previous_spent
from
    (select 
       x.month as month ,
       y.type  as type
     from
        (select distinct month
         from current_expense) x
         cross join 
           (select distinct type 
            from current_expense) y) z
    left outer join current_expense c
    on z.month = c.month and
       z.type  = z.type
    left outer join previous_expense p
    on z.type = p.type;