sql嵌套选择

Question

我是sql的新手，我了解这里的总体情况，但我无法详细解释。我想，

从lookupday表中获取的lookupseekid值减少-1，并分配给t2表的lookupeekid。其中，t1.lookupeekid=t2.lookupheekid和t1.weekdaynumber=1。start_of_week被导入到表t3中。

你觉得我的想法怎么样，是真的吗？

(select dateoftransaction
from lookupday t1,
(select lookupweekid-1 from lookupday 
where dateoftransaction = date) t2 (lookupweekid)
where t1.lookupweekid=t2.lookupweekid
and t1.weekdaynumber=1) t3 (start_of_week)

Answer 1

我猜它在计算前一周的开始。

也许t3子查询也可以这样写：

select dateoftransaction
from lookupday
where lookupweekid in (select lookupweekid - 1
from lookupday 
where dateoftransaction = current_date)
and weekdaynumber = 1