在完全连接postgresql中选择非空列

Question

我有3张桌子：

with current_exclusive as(
        select id_station, area_type, 
    count(*) as total_entries
    from c1169.data_cashier
    where id_station IN(2439,2441,2443,2445,2447,2449) and date >= '2017-10-30' and date <= '2017-12-30' 
    group by id_station, area_type
), current_table as(
        select id_station, area_type, 
    sum(total_time) filter (where previous_status = 1) as total_time
    from c1169.data_table
    where id_station IN(2439,2441,2443,2445,2447,2449) and date >= '2017-10-30' and date < '2017-12-30' 
    group by id_station, area_type
), current_cashier as(
        select id_station, area_type, 
    sum(1) as total_transactions
    from c1169.data_cashier
    where id_station IN(2439,2441,2443,2445,2447,2449) and date >= '2017-10-30' and date < '2017-12-30' 
    group by id_station, area_type
)
select *
from current_exclusive
full join current_table on current_exclusive.id_station = current_table.id_station and current_exclusive.area_type = current_table.area_type
full join current_cashier on current_exclusive.id_station = current_cashier.id_station and current_exclusive.area_type = current_cashier.area_type

结果是：

但我的预期结果是：

有没有办法选择*并显示预期的结果？因为当我进行完全连接时，id_station和area_type在某些表中可能为null，因此很难选择哪个列不为null。
比如：select case id_station is not null then id_station else id_station1 end，但我有多达10个表，所以在select case

中无法做到

Answer 1

如果您坚持使用select *，则无法完成任何操作，因为您从不同的表中获取值。

您拥有的选项是添加COALESCE块，该列为您提供列列表中的第一个non-null值。

所以，你可以使用。

select COALESCE( current_exclusive.id_station, current_table.id_station, current_cashier.id_station ) as id_station , 
COALESCE( current_exclusive.area_type , current_table.area_type, current_cashier.area_type ) as area_type ,.....
...
from current_exclusive
full join current_table..
...

Answer 2

根据the documentation:

使用USING

  

使用（join_column [，...]）

     

USING（a，b，...）形式的一个子句是ON left_table.a = right_table.a和left_table.b = right_table.b ....的简写。另外，USING意味着每个只有一个一对等效列将包含在连接输出中，而不是两者。

select *
from current_exclusive
full join current_table using (id_station, area_type)
full join current_cashier using (id_station, area_type)