Getting data from the last 12 month using mysql - mysql

Question

I have the following data structure in my table:
id member_from member_till
1 2014/03/01 2014/05/18
2 2014/01/09 2014/08/13
...
How can i get a count of active members for the last 12 month, grouped by month?
Ex:
...
2014/12/01,5
2015/01/01,12
As a future development is it possible to make the count the average of the first and last day of each month?

Answer 1

First of all you need the last twelve months. Then outer-join the members and count those where the month is in the membership range.
select
date_format(all_months.someday, '%Y %m') as mymonth,
count(membership.member_from) as members
from
(
select current_date as someday
union all
select date_add(current_date, interval -1 month)
union all
select date_add(current_date, interval -2 month)
union all
select date_add(current_date, interval -3 month)
union all
select date_add(current_date, interval -4 month)
union all
select date_add(current_date, interval -5 month)
union all
select date_add(current_date, interval -6 month)
union all
select date_add(current_date, interval -7 month)
union all
select date_add(current_date, interval -8 month)
union all
select date_add(current_date, interval -9 month)
union all
select date_add(current_date, interval -10 month)
union all
select date_add(current_date, interval -11 month)
) all_months
left join membership
on date_format(all_months.someday, '%Y %m')
between
date_format(membership.member_from, '%Y %m')
and
date_format(membership.member_till, '%Y %m')
group by date_format(all_months.someday, '%Y %m');
SQL fiddle: http://www.sqlfiddle.com/#!2/6dc5a/10.
As to your future requirement: You can join the membership table twice, once for the members on the first of a month, once for the last of the month (loosing those who participated only some days in the middle of a month). Then add both counts and divide by two.

Answer 2

You can try with SQL Query:
SELECT `member_from`, count(id) FROM tbl_test WHERE `member_from` BETWEEN <From date> AND <To date> GROUP BY `member_from`;

Answer 3

Complete with future requirement:
SELECT
d.ymonth,
COUNT(m.member_from) total,
COALESCE(SUM(d.fday BETWEEN m.member_from AND m.member_till), 0) total_fom,
COALESCE(SUM(d.lday BETWEEN m.member_from AND m.member_till), 0) total_lom
FROM
(
SELECT
CAST(#first_day := #first_day + INTERVAL 1 MONTH AS DATE) fday,
LAST_DAY(#first_day) lday,
DATE_FORMAT(#first_day, '%Y-%m') ymonth
FROM
information_schema.collations
CROSS JOIN
(SELECT #first_day := LAST_DAY(CURRENT_DATE) - INTERVAL 13 MONTH + INTERVAL 1 DAY) x
LIMIT 12
) d
LEFT JOIN
membership m
ON d.lday >= m.member_from
AND d.fday <= m.member_till
GROUP BY d.ymonth
The subquery generates a virtual lookup table with 3 columns:
+ ---------- + ---------- + ------- +
| fday | lday | ymonth |
+ ---------- + ---------- + ------- +
| 2014-02-01 | 2014-02-28 | 2014-02 |
| \/ | \/ | \/ |
| 2015-01-01 | 2015-01-31 | 2015-01 |
+ ---------- + ---------- + ------- +
Then the membership table can be joined on the overlaps member_from-member_till and the beginning and ending of each month.