Question

这是产生以下数据。到现在为止还挺好。我需要找到cte的max（list_price）。我是否应该将以下所有代码视为新的＆＃34; cte2＆＃34;并找到最大的？我尝试使用＆＃34; max（BK.list_price）＆＃34;在外部查询中，但我无法计算Group By。（使用SQLS 2008 R2）

with cte as
(
  select BT.book_id
  from
    bkinfo.book_topics BT
  where
    BT.topic_id = 'DB'    
)
select BK.book_id, BK.list_price
from bkinfo.books BK
where BK.book_id in
(
  select cte.book_id
  from cte
)
;
go

book_id                              list_price
----------- ---------------------------------------
1105                                   59.95
1108                                   39.95
1109                                   80.00
  .
  .
  .

Answer 1

你真的不需要CTE：

select MAX(BK.list_price)
from bkinfo.books BK
where exists
(
    select BT.book_id
    from bkinfo.book_topics BT
    where BT.topic_id = 'DB'
    and BT.book_id = BK.book_id
)

Answer 2

您需要同时携带book_id及其价格，价格在主题中最高。这可能有点矫枉过正，但总的来说，您可能希望找到每个主题最Nth本书最贵的书：

with cteBookCostsPerTopic as
(
  select 
     BT.book_id, BK.list_price, BT.topic_id,
     ROW_NUMBER() OVER (PARTITION BY BT.topic_ID ORDER BY list_price DESC) as Rnk
  from
    books BK
    INNER JOIN book_topics BT
      ON BT.book_id = BK.book_ID
)
SELECT topic_id, book_id, list_price
  FROM cteBookCostsPerTopic
  WHERE  Rnk=1-- i.e. most expensive
         and topic_id = 'DB'

Fiddle here

在CTE中找到最大值

2 个答案: