有没有办法在连接子句中执行 If Then 语句

Question

我有两个表，spend 和 bookings，我正在尝试对其进行完全连接。由于表格的性质（并非所有预订都有支出，也并非所有支出都有 booking_id，有时会分配错误的 booking_id），我想在加入子句。

select bk.booking_id, bk.company_id, bk.event_id, bk.total_amount_booked, sp.spend
from 
(select booking_id, company_id, event_id, booked_rate, total_amount_booked
from bookings) bk
full join
(select booking_id, company_id, event_id, normalized_spend, spend
from spend) sp
on (bk.booking_id = sp.booking_id and bk.booked_rate = sp.normalized_spend)
or (bk.company_id = sp.company_id and bk.event_id = sp.event_id);

基本上，如果 booking_id 匹配且标准化支出与 booked_rate 匹配，则在该条件下加入。如果没有，请加入 company_id 和 event_id。

但是，执行此查询 returns

FULL JOIN is only supported with merge-joinable join conditions;

有更好的方法吗？使用 Redshift

Answer 1

这有点麻烦，但您可以用两个 left joins 和 union all 模拟 full 连接：

select bk.booking_id, bk.company_id, bk.event_id, bk.total_amount_booked, sp.spend
from bookings bk
left join spend sp
    on (bk.booking_id = sp.booking_id and bk.booked_rate = sp.normalized_spend)
    or (bk.company_id = sp.company_id and bk.event_id = sp.event_id)
union all
select bk.booking_id, bk.company_id, bk.event_id, bk.total_amount_booked, sp.spend
from spend sp
left join bookings bk
    on (bk.booking_id = sp.booking_id and bk.booked_rate = sp.normalized_spend)
    or (bk.company_id = sp.company_id and bk.event_id = sp.event_id)
where bk.booking_id is null

Answer 2

也许使用 CASE 语句，例如

...ON CASE WHEN (bk.booking_id = sp.booking_id and bk.booked_rate = sp.normalized_spend)
          THEN (bk.booking_id = sp.booking_id and bk.booked_rate = sp.normalized_spend)
         WHEN (bk.company_id = sp.company_id and bk.event_id = sp.event_id) 
          THEN (bk.company_id = sp.company_id and bk.event_id = sp.event_id)
    END

有没有办法在连接子句中执行 If Then 语句

Is there a way to do an If Then statement in the join clause

sql

left-join

where-clause

full-outer-join

amazon-redshift