I want to select rows from my Postgres database that meet the following criteria:
So if I had a table like this:
User | Item | Date -----+------+------ Fred | Ball | 5/1/2015 Jane | Pen | 5/7/2015 Fred | Cup | 5/11/2015 Mike | Ball | 5/13/2015 Jane | Ball | 5/18/2015 Fred | Pen | 5/20/2015 Jane | Bat | 5/22/2015The search might be "what did people buy after they bought a ball?" The output I would want would be:
\nUser | Item | Date \n-----+------+------ \nFred | Cup | 5/11/2015 \nFred | Pen | 5/20/2015 \nJane | Bat | 5/22/2015 \n
I've gotten as far as SELECT * FROM orders AS or WHERE or.user IN (SELECT or2.second_id FROM orders AS or2 GROUP BY or2.user HAVING count(*) > 1);
, which gives me all of Fred's and Jane's orders (since they ordered multiple things). But when I try to put additional limitations on the WHERE clause (eg SELECT * FROM orders AS or WHERE or.item = 'Ball' AND or.user IN (SELECT or2.second_id FROM orders AS or2 GROUP BY or2.user HAVING count(*) > 1);
, I get something that isn't what I expect at all -- a list of records where item = 'Ball' that seems to have ignored the second part of the query.
Thanks for any help you can provide.
Edit: Sorry, I misled some people at the end by describing the bad approach I was taking. (I was working on getting a list of the Ball purchases, which I could use as a subquery in a next step, but people correctly noted that this is an unnecessarily complex/expensive approach.)
I think this might give the result you are looking for:
SELECT orders.user, orders.item, orders.date
FROM orders, (SELECT * FROM orders WHERE item = 'ball') ball_table
WHERE orders.user = ball_table.user AND orders.date > ball_table.date;
select b.*
from user_table a
join user_table b
on b.user = a.user
and b.date > a.date
and b.item = 'Ball'
SELECT DISTINCT t3.*
FROM mytable t1
INNER JOIN mytable t2
ON t1.Item = t2.Item AND t1.User <> t2.User
INNER JOIN mytable t3
ON t2.User = t3.User AND t2.Date <= t3.Date
WHERE t1.Item = "Ball"
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