Efficient sql subquery on same table based off datetime value - sql

Question

Below I have a simple query to get all the movie ratings for today joining an "event" table and "movie" table.
Select e.*, m.moviename
From Event e, movie m
Where e.eventdate >= DATEADD(day, -1, GETDATE())
and e.moviekey = m.moviekey
order by e.Ratings desc;
Question
In the example above, how would you retrieve the ratings from 1 week ago, and 1 month ago. So the query would return 2 extra columns RatingOneMonthAgo, RatingsOneWeekAgo,etc.
I've looked into subqueries and it's not clicking any help would be appreciated.
Thanks

Answer 1

You could use CTEs to pull this information in (similar to using subqueries).
The following query assumes that you having ratings for every day, and no duplicates (multiple ratings for the same movie on the same day):
WITH cteOneWeekAgo
AS
(
SELECT
moviekey
, Ratings
FROM Event
WHERE CAST(eventdate AS date) = DATEADD(WEEK, -1, CAST(GETDATE() AS date))
)
,
cteOneMonthAgo
AS
(
SELECT
moviekey
, Ratings
FROM Event
WHERE CAST(eventdate AS date) = DATEADD(MONTH, -1, CAST(GETDATE() AS date))
)
SELECT
e.*
, m.moviename
, w.Ratings Ratings_OneWeekAgo
, mth.Ratings Ratings_OneMonthAgo
FROM
Event e
JOIN movie m ON e.moviekey = m.moviekey
LEFT JOIN cteOneWeekAgo w ON e.moviekey = w.moviekey
LEFT JOIN cteOneMonthAgo mth ON e.moviekey = mth.moviekey
WHERE e.eventdate >= DATEADD(DAY, -1, GETDATE())
ORDER BY e.Ratings DESC
I also wrote a more complex query, which will pull in the most recent ratings for the movie before the date you're looking for if ratings for that date don't exist.
WITH cteOneWeekAgo
AS
(
SELECT
moviekey
, Ratings
, eventdate
FROM
(
SELECT
moviekey
, Ratings
, eventdate
, ROW_NUMBER() OVER (PARTITION BY moviekey ORDER BY eventdate DESC) R
FROM Event
WHERE CAST(eventdate AS date) <= DATEADD(WEEK, -1, CAST(GETDATE() AS date))
) Q
WHERE R = 1
)
,
cteOneMonthAgo
AS
(
SELECT
moviekey
, Ratings
, eventdate
FROM
(
SELECT
moviekey
, Ratings
, eventdate
, ROW_NUMBER() OVER (PARTITION BY moviekey ORDER BY eventdate DESC) R
FROM Event
WHERE CAST(eventdate AS date) <= DATEADD(MONTH, -1, CAST(GETDATE() AS date))
) Q
WHERE R = 1
)
SELECT
e.*
, m.moviename
, w.eventdate Ratings_OneWeekAgo_MostRecentDate
, w.Ratings Ratings_OneWeekAgo
, mth.eventdate Ratings_OneMonthAgo_MostRecentDate
, mth.Ratings Ratings_OneMonthAgo
FROM
Event e
JOIN movie m ON e.moviekey = m.moviekey
LEFT JOIN cteOneWeekAgo w ON e.moviekey = w.moviekey
LEFT JOIN cteOneMonthAgo mth ON e.moviekey = mth.moviekey
WHERE e.eventdate >= DATEADD(DAY, -1, GETDATE())
ORDER BY e.Ratings DESC