I have two tables from a site similar to SO: one with posts, and one with up/down votes for each post. I would like to select all votes cast on the day that a post was modified.
My tables layout is as seen below:
Posts:
-----------------------------------------------
| post_id | post_author | modification_date |
-----------------------------------------------
| 0 | David | 2012-02-25 05:37:34 |
| 1 | David | 2012-02-20 10:13:24 |
| 2 | Matt | 2012-03-27 09:34:33 |
| 3 | Peter | 2012-04-11 19:56:17 |
| ... | ... | ... |
-----------------------------------------------
Votes (each vote is only counted at the end of the day for anonymity):
-------------------------------------------
| vote_id | post_id | vote_date |
-------------------------------------------
| 0 | 0 | 2012-01-13 00:00:00 |
| 1 | 0 | 2012-02-26 00:00:00 |
| 2 | 0 | 2012-02-26 00:00:00 |
| 3 | 0 | 2012-04-12 00:00:00 |
| 4 | 1 | 2012-02-21 00:00:00 |
| ... | ... | ... |
-------------------------------------------
What I want to achieve:
-----------------------------------
| post_id | post_author | vote_id |
-----------------------------------
| 0 | David | 1 |
| 0 | David | 2 |
| 1 | David | 4 |
| ... | ... | ... |
-----------------------------------
I have been able to write the following, but it selects all votes on the day before the post modification, not on the same day (so, in this example, an empty table):
SELECT Posts.post_id, Posts.post_author, Votes.vote_id
FROM Posts
LEFT JOIN Votes ON Posts.post_id = Votes.post_id
WHERE CAST(Posts.modification_date AS DATE) = Votes.vote_date;
How can I fix it so the WHERE clause takes the day before Votes.vote_date? Or, if not possible, is there another way?
Depending on which type of database you are using (SQL, Oracle ect..);To take the Previous days votes you can usually just subtract 1 from the date and it will subtract exactly 1 day:
Where Cast(Posts.modification_date - 1 as Date) = Votes.vote_date
or if modification_date is already in date format just:
Where Posts.modification_date - 1 = Votes.vote_date
If you have a site similar to Stack Overflow, then perhaps you also use SQL Server:
SELECT p.post_id, p.post_author, v.vote_id
FROM Posts p LEFT JOIN
Votes v
ON p.post_id = v.post_id
WHERE CAST(DATEDIFF(day, -1, p.modification_date) AS DATE) = v.vote_date;
Different databases have different ways of subtracting one day. If this doesn't work, then your database has something similar.
I found another solution, which is to add a day to Posts.modification_date:
...
WHERE CAST(CEILING(CAST(p.modification_date AS FLOAT)) AS datetime) = v.vote_date
Related
Hope you can help. We have a table with two columns Customer_ID and Trip_Date. The customer receives 15% off on their first visit and on every visit where they haven't received the 15% off offer in the past thirty days. How do I write a single SQL query that finds all days where a customer received 15% off?
The table looks like this
+-----+-------+----------+
| Customer_ID | date |
+-----+-------+----------+
| 1 | 01-01-17 |
| 1 | 01-17-17 |
| 1 | 02-04-17 |
| 1 | 03-01-17 |
| 1 | 03-15-17 |
| 1 | 04-29-17 |
| 1 | 05-18-17 |
+-----+-------+----------+
The desired output would look like this:
+-----+-------+----------+--------+----------+
| Customer_ID | date | received_discount |
+-----+-------+----------+--------+----------+
| 1 | 01-01-17 | 1 |
| 1 | 01-17-17 | 0 |
| 1 | 02-04-17 | 1 |
| 1 | 03-01-17 | 0 |
| 1 | 03-15-17 | 1 |
| 1 | 04-29-17 | 1 |
| 1 | 05-18-17 | 0 |
+-----+-------+----------+--------+----------+
We are doing this work in Netezza. I can't think of a way using just window functions, only using recursion and looping. Is there some clever trick that I'm missing?
Thanks in advance,
GF
You didn't tell us what your backend is, nor you gave some sample data and expected output nor you gave a sensible data schema :( This is an example based on guess of schema using postgreSQL as backend (would be too messy as a comment):
(I think you have Customer_Id, Trip_Date and LocationId in trips table?)
select * from trips t1
where not exists (
select * from trips t2
where t1.Customer_id = t2.Customer_id and
t1.Trip_Date > t2.Trip_Date
and t1.Trip_date - t2.Trip_Date < 30
);
I have the following sample table:
+----------+------+-------+
| DATE | NAME | HOURS |
+----------+------+-------+
| 2018-5-3 | JOHN | 8 |
+----------+------+-------+
| 2018-5-9 | JOHN | 5 |
+----------+------+-------+
How can I generate a query that fills new rows to the existent data, e.g, sample query result:
+-----------+------+-------+
| DATE | NAME | HOURS |
+-----------+------+-------+
| 2018-5-1 | JOHN | 0 |
+-----------+------+-------+
| 2018-5-2 | JOHN | 0 |
+-----------+------+-------+
| 2018-5-3 | JOHN | 8 |
+-----------+------+-------+
| 2018-5-4 | JOHN | 0 |
+-----------+------+-------+
| 2018-5-5 | JOHN | 0 |
+-----------+------+-------+
| 2018-5-6 | JOHN | 0 |
+-----------+------+-------+
| 2018-5-7 | JOHN | 0 |
+-----------+------+-------+
| 2018-5-8 | JOHN | 0 |
+-----------+------+-------+
| 2018-5-9 | JOHN | 5 |
+-----------+------+-------+
| 2018-5-10 | JOHN | 0 |
+-----------+------+-------+
Check that I've added 0 into HOURS column because JOHN doesn't appear with hours in the specified date (only in 2018-5-3 and 2018-5-8). I am currently trying to get this result. This is only the begin of a big table I need to process, so I'll need to generate this fixed values per user. I was trying using left/right join with previously generated dates but it didn't work.
Can you advice me the best way to accomplish it? Thanks.
Use generate_series() and left join:
select g.dte, t.name, coalesce(t.hours, 0) as hours
from generate_series('2018-05-01'::date, '2018-05-10'::date, interval '1 day') g(dte) left join
t
on g.dte = t.date;
For multiple users, you need to generate all the rows for all the users and then left join:
select g.dte, n.name, coalesce(t.hours, 0) as hours
from generate_series('2018-05-01'::date, '2018-05-10'::date, interval '1 day'
) g(dte) cross join
(select distinct name from t) n left join
t
on g.dte = t.date and n.name = t.name;
I have two MS Access tables sharing a one to many relationship. Their structures are like the following:
tbl_Persons
+----------+------------+-----------+
| PersonID | PersonName | OtherData |
+----------+------------+-----------+
| 1 | PersonA | etc. |
| 2 | PersonB | |
| 3 | PersonC | |
tbl_Visits
+----------+------------+------------+-----------------------
| VisitID | PersonID | VisitDate | dozens of other fields
+----------+------------+------------+-----------
| 1 | 1 | 09/01/13 |
| 2 | 1 | 09/02/13 |
| 3 | 2 | 09/03/13 |
| 4 | 2 | 09/04/13 | etc...
I wish to create a new table based on the VisitDate field, the column headings of which are Visit-n where n is 1 to the number of visits, Visit-n-Data1, Visit-n-Data2, Visit-n-Data3 etc.
MergedTable
+----------+----------+---------------+-----------------+----------+----------------+
| PersonID | Visit1 | Visit1Data1 | Visit1Data2... | Visit2 | Visit2Data1... |
+----------+----------+---------------+-----------
| 1 | 09/01/13 | | | 09/02/13 |
| 2 | 09/03/13 | | | 09/04/13 |
| 3 | etc. | |
I am really not sure how to do this. Whether SQL query or using DAO then looping through records and columns. It is essential that there is only 1 PersonID per row and all his data appears chronologically into columns.
Start of by ranking the visits with something like
SELECT PersonID, VisitID,
(SELECT COUNT(VisitID) FROM tbl_Visits AS C
WHERE C.PersonID = tbl_Visits.PersonID
AND C.VisitDate < tbl_Visits.VisitDate) AS RankNumber
FROM tbl_Visits
Use this query as a base for the 'pivot'
Since you seem to have some visits of persons on the same day (visit 1 and 2) the WHERE clause needs to be a bit more sophisticated. But I hope you get the basic concept.
Pivoting can be done with multiple LEFT JOINs.
I question if my solution will have a high performance, since I did not test it. It is easier in SQL Server than in MS Access to accomplish.
I have table in database called fileupload_share.
+----+----------+----------+----------------+----------------------------------+
| id | users_id | files_id | shared_user_id | shared_date |
+----+----------+----------+----------------+----------------------------------+
| 3 | 1 | 1 | 2 | 2013-01-31 14:27:06.523908+00:00 |
| 2 | 1 | 1 | 2 | 2013-01-31 14:25:37.760192+00:00 |
| 4 | 1 | 3 | 2 | 2013-01-31 14:46:01.089560+00:00 |
| 5 | 1 | 1 | 3 | 2013-01-31 14:50:54.917337+00:00 |
I want to count the number of shared_user_id according to the file_id.
For example I want to find with how many users the file with id 1 is shared. The answer is with 2 users(shared_user_id). How can I find that in Django?
file_id = 2 #Here is your file_id variable
fileupload_share.objects.filter(file_id = file_id)
.order_by('shared_user_id').distinct('shared_user_id').count()
As comments below say this example doesn't work on MySQL, because of distinct method on field.
However you can try danihp's method:
file_id = 2 #Here is your file_id variable
fileupload_share.objects.filter(file_id = file_id)
.values_list('shared_user_id', flat=True).distinct().count()
Can you please help me build an SQL query to retrieve data from a history table?
I'm a newbie with only a one-week coding experience. I've been trying simple SELECT statements so far but have hit a stumbling block.
My football club's database has three tables. The first one links balls to players:
BallDetail
| BallID | PlayerID | TeamID |
|-------------------|--------|
| 1 | 11 | 21 |
| 2 | 12 | 22 |
The second one lists things that happen to the balls:
BallEventHistory
| BallID | Event | EventDate |
|--------|------ |------------|
| 1 | Pass | 2012-01-01 |
| 1 | Shoot | 2012-02-01 |
| 1 | Miss | 2012-03-01 |
| 2 | Pass | 2012-01-01 |
| 2 | Shoot | 2012-02-01 |
And the third one is a history change table. After a ball changes hands, history is recorded:
HistoryChanges
| BallID | ColumnName | ValueOld | ValueNew |
|--------|------------|----------|----------|
| 2 | PlayerID | 11 | 12 |
| 2 | TeamID | 21 | 22 |
I'm trying to obtain a table that would list all passes and shoots Player 11 had done to all balls before the balls went to other players. Like this:
| PlayerID | BallID | Event | Month |
|----------|--------|-------|-------|
| 11 | 1 | Pass | Jan |
| 11 | 1 | Shoot | Feb |
| 11 | 2 | Pass | Jan |
I begin so:
SELECT PlayerID, BallID, Event, DateName(month, EventDate)
FROM BallDetail bd INNER JOIN BallEventHistory beh ON bd.BallID = beh.BallID
WHERE PlayerID = 11 AND Event IN (Pass, Shoot) ...
But how to make sure that Ball 2 also gets included despite being with another player now?
Select PlayerID,BallID,Event,datename(month,EventDate) as Month,Count(*) as cnt from
(
Select
Coalesce(
(Select ValueNew from #HistoryChanges where ChangeDate=(Select max(ChangeDate) from #HistoryChanges h2 where h2.BallID=h.BallID and ColumnName='PlayerID' and ChangeDate<=EventDate) and BallID=h.BallID and ColumnName='PlayerID')
,(Select PlayerID from #BallDetail where BallID=h.BallID)
) as PlayerID,
h.BallID,h.Event,EventDate
from #BallEventHistory h
) a
Group by PlayerID, BallID, Event,datename(month,EventDate)
SELECT d.PlayerID, d.BallID, h.Event, DATENAME(mm, h.EventDate) AS Month
FROM BallDetail d JOIN BallEventHistory h ON d.BallID = h.BallID
WHERE h.Event IN ('Pass', 'Shoot') AND d.PlayerID = 11
OR EXISTS (SELECT 1
FROM dbo.HistoryChanges c
WHERE c.ValueOld = 11 AND c.ValueNew = d.PlayerID AND c.ColumnName = 'PlayerID' and c.ChangeDate = h.EventDate)