如何在一个查询/表中获取2个字段的唯一值列表？

Question

代表。我有这个查询

select distinct t1.date1, t2.date2
from t1
join t2 ...
....
where ...

我希望得到这2个日期的唯一值列表。我怎么能在Firebird 2.5上做到这一点？

我试试这个

with dates as (
select t1.date1 d1, t2.date2 d2
from t1
join t2 ...
....
where ...)
select d1 from dates
union
select d2 from dates

但是这个版本会使性能降低两倍

Answer 1

试试这个：

with dates (dt) as (
  select t1.date1 from t1
  where (1=1) --conditions

  union

  select t2.date2 from t2
  where (1=1) --conditions
)

select unique dt
from dates