在Oracle中声明和设置日期

Question

我知道在sql server中我可以通过以下方式声明日期：

declare @last_thursday date, @this_wednesday
set @last_thursday = '15-feb-2018'
set @this_wednesday = '21-feb-2018'

select name
from my_table
where upd_date between @last_thursday and @this_wednesday

但是我怎样才能在Oracle中做同样的工作呢？