How to pass parameters in subquery mysql? - mysql

Question

So, I have a mysql table with user id(id) and date of transaction(dot) that looks like:
id dot
-------------------------------
101 2015-06-12 12:18:42 UTC
102 2015-06-12 12:18:40 UTC
103 2015-06-12 12:18:42 UTC
101 2015-07-12 12:18:42 UTC
and so on.
(Output for this data should be:
Year Month Num of users
-----------------------------
2015 06 0
2015 07 2
)
It logs all the transactions that are made. For each month m, I want to find out the count of users by month and year who transacted in m-1 month but not in m month. The results need to be grouped by year and month. Ideally, table should look like (http://sqlfiddle.com/#!9/b80f49/1)
Year Month Num of users
-----------------------------
2015 05 0
2015 06 2
2015 07 1
2015 08 4
Now for a single month(E.g. 05/2015), I can hardcode:
SELECT "2015" AS Year,"05" AS Month, "COUNT(DISTINCT id) FROM table WHERE
MONTH(dot)=4 AND YEAR(dot)=2015
AND id NOT IN
(SELECT id FROM table WHERE MONTH(dot)=5 AND YEAR(dot)=2015)
To group the count of users using GROUP BY, the query would look like:
SELECT YEAR(dot) as Year,MONTH(dot),COUNT(DISTINCT id) as Month FROM table
WHERE id NOT IN(SELECT id FROM table
WHERE DATEDIFF(dot_parent,dot_this_table)<30 AND DATEDIFF(dot_parent,dot_this_table)>=0)
Here dot_parent is the dot of the parent query and dot_this_table is the dot of the subquery. Now the problem here is that I can't pass the dot_parent inside the subquery. Is there a way to do that or frame the query in another way such that its logical structure remains similar, since I would have to make similar queries for multiple date ranges.

Answer 1

You must query the same table thrice: once for the months to show, once to find the users in the previous months, once for user matches in the months in question. You'd select distinct users per month, as you are not interested in whether a user had more than one transaction in a month or not.
Here is the complete query:
select
this_month.year,
this_month.month,
count(prev_month_users.user) - count(this_month_users.user) as users
from
(
select distinct year(timing) as year, month(timing) as month
from transactions
) this_month
left join
(
select distinct
year(timing) as year, month(timing) as month, id as user,
year(date_add(timing, interval 1 month)) as next_month_year,
month(date_add(timing, interval 1 month)) as next_month_month
from transactions
) prev_month_users
on prev_month_users.next_month_year = this_month.year
and prev_month_users.next_month_month = this_month.month
left join
(
select distinct year(timing) as year, month(timing) as month, id as user
from transactions
) this_month_users
on this_month_users.user = prev_month_users.user
and this_month_users.year = prev_month_users.next_month_year
and this_month_users.month = prev_month_users.next_month_month
group by this_month.year, this_month.month;
Result:
year month users
2015 5 0
2015 6 2
2015 7 1
2015 8 3
Note that I show three users for August (users 101, 102, 104). User 101 had two transactions in July, but it is still three users who had transactions in July but not in August.
Here is your SQL fiddle back: http://sqlfiddle.com/#!9/b80f49/13