sql-聚合最大功能和分组依据

Question

select city, title, releasedate
from movies join shownat on shownat.movietitle = movies.title join theatres on theatres.theatrename = shownat.theatrename
group by city, title, releasedate
order by city, max(releasedate) desc;

上面是我的查询，这个问题要解决。

查找每个城市显示的最新电影的标题。 显示城市名称和最新电影名称（按城市名称和电影名称排序）。

归一化的数据有3个表，分别称为剧院，电影院和电影院。 是的，我知道上图所示的发布日期可能会更有效，对我来说更有意义，因为并非总是在同一时间在同一地区或城市发布视频。 但是，这是我坚持的最后一个家庭作业问题。 需要的是该城市应该只有1个列表。 我认为按城市分组将解决这个问题。 对于每个城市，我需要数据集中每个特定城市（4）中具有最新发行日期的电影的标题。 我不确定为什么当我具有按此功能的group by功能及其用于处理合计max函数时，为什么在这里得到重复。 max函数应该只是给我最新版本？

"CITY"          "TITLE"        "RELEASEDATE"
"Cincinnati"    "Interstellar"  07-NOV-14
"Cincinnati"    "Big Hero 6"    07-NOV-14
"Cincinnati"    "Nightcrawler"  31-OCT-14
"Cincinnati"    "Gone Girl"     03-OCT-14
"Cincinnati"    "The Pianist"   03-JAN-03
"Cincinnati"    "Fargo" 05-APR-96
"Cincinnati"    "Schindler's List"  04-FEB-94
"Florence"      "Big Hero 6"    07-NOV-14
"Florence"      "Interstellar"  07-NOV-14
"Florence"      "Nightcrawler"  31-OCT-14
"Florence"  "Gone Girl" 03-OCT-14
"Florence"  "District 9"    14-AUG-09
"Florence"  "A Perfect Getaway" 07-AUG-09
"Florence"  "Aliens in the Attic"   31-JUL-09
"Florence"  "Away We Go"    26-JUN-09
"Florence"  "Up"    29-MAY-09
"Florence"  "Star Trek" 08-MAY-09
"Florence"  "The Hurt Locker"   10-OCT-08
"Florence"  "The Dark Knight"   18-JUL-08
"Florence"  "The Departed"  06-OCT-06
"Florence"  "The Green Mile"    10-DEC-99
"Newport"   "Interstellar"  07-NOV-14
"Newport"   "Big Hero 6"    07-NOV-14
"Newport"   "Gone Girl" 03-OCT-14
"Newport"   "District 9"    14-AUG-09
"Newport"   "A Perfect Getaway" 07-AUG-09
"Newport"   "Away We Go"    26-JUN-09
"Newport"   "Up"    29-MAY-09
"Newport"   "The Departed"  06-OCT-06
"Wilder"    "Big Hero 6"    07-NOV-14
"Wilder"    "Interstellar"  07-NOV-14
"Wilder"    "Gone Girl" 03-OCT-14
"Wilder"    "Public Enemies"    01-JUL-09
"Wilder"    "The Departed"  06-OCT-06

Answer 1

这将是查询，但我不确定max函数是否可以与日期变量一起使用：

SELECT city, title, max (releasedate) as max_dateRelease
FROM movies inner join shownat on shownat.movietitle = movies.title join theatres 
on theatres.theatrename = shownat.theatrename
GROUP BY city, title, releasedate
ORDER BY city, max_dateRelease desc

Answer 2

select T1.city,T2.movietitle,T1.releasedate
from
(select city,max(releasedate) as maxreleasedate
from movies join shownat on shownat.movietitle = movies.title join theatres on theatres.theatrename = shownat.theatrename
group by city) as T1
inner join
(select shownat.movietitle,shownat.city,shownat.releasedate)
from shownat) as T2
 on T1.city=T2.city and T1.maxreleasedate=T2.releasedate

这是一种方法，也不是最佳方法。