mysql index guidance needed - group by sub query super slow - mysql

Question

Quick overview, I have worked out a mysql query but need to optimize the performance.
My original post was here but its gone cold and im getting desperate to elaborate on some of the suggestions which I tried to implement. So its not a dupe post but it is related.
Here is the query that takes 45 seconds plus, the group by on the second sub query really slows things down.
SELECT * FROM
(
SELECT DISTINCT email,
title,
first_name,
last_name,
'chauntry' AS source,
post_code AS postcode
FROM chauntry
WHERE mailing_indicator = 1
) AS x
JOIN
(
SELECT email,
Avg(amount_paid) AS avg_paid,
Count(*) AS no_times_booked,
Count(DISTINCT( Date_format(added, '%M %Y') )) AS unique_months
FROM chauntry
WHERE added >= Now() - INTERVAL 1 year
GROUP BY email
) AS y
ON x.email = y.email
Based on the index suggestions from here I looked around for a few examples of indexing and came up with the below
ALTER TABLE `chauntry`
ADD INDEX(`mailing_indicator`, `email`);
ALTER TABLE `chauntry`
ADD INDEX covering_index (`added`, `email`, `amount_paid`);
This makes no difference to the query time and im not sure if what im doing is even close as up until now I have had no need to use indexing.
suggestions welcome on how to index my table correctly or how to modify the query.

Answer 1

Out of curiousity, does this query do what you want?
SELECT email, title, first_name, last_name, 'chauntry' AS source,
post_code AS postcode,
Avg(amount_paid) AS avg_paid,
Count(*) AS no_times_booked,
Count(DISTINCT( Date_format(added, '%M %Y') )) AS unique_months
FROM chauntry
WHERE added >= Now() - INTERVAL 1 year
GROUP BY email, title, first_name, last_name, post_code
HAVING SUM(mailing_indicator = 1) > 0;
It would seem to follow the same logic as your query, except that the mailing indicator would need to have been set in the past year.

Answer 2

Why use JOIN on subselects to same table?
I would try this:
SELECT email,
title,
first_name,
last_name,
'chauntry' AS source,
post_code AS postcode
Avg(amount_paid) AS avg_paid,
Count(*) AS no_times_booked,
Count(DISTINCT( Date_format(added, '%M %Y') )) AS unique_months
FROM chauntry
WHERE
mailing_indicator = 1 and
added >= Now() - INTERVAL 1 year
GROUP BY email
Also I don't think you need any index with query like this, maybe on added and email, but you already added them.

Answer 3

Minor play.
The average of the amount_paid is the biggest problem. If you are prepared to put up with the possibility of an inaccuracy for this figure then you could maybe average the distinct values of the amount_paid field. This WILL give the wrong value under certain circumstances (ie, if you had 100 bookings, 99 at $1 and 1 at $100 the average would be given as $50.50 rather than $1.99), but if the amount paid is never repeated then this may be acceptable.
Otherwise you can probably use a join of the table against itself. To get the no_times_booked you can count the DISTINCT unique identifiers of the table (I have assumed id here).
SELECT c1.email,
c1.title,
c1.first_name,
c1.last_name,
'chauntry' AS source,
c1.post_code AS postcode
Avg(DISTINCT c2.amount_paid) AS avg_paid,
Count(DISTINCT c2.id) AS no_times_booked,
Count(DISTINCT( Date_format(c2.added, '%M %Y') )) AS unique_months
FROM chauntry c1
INNER JOIN chauntry c2
ON c1.email = c2.email
WHERE c1.mailing_indicator = 1
AND c2.added >= Now() - INTERVAL 1 year
GROUP BY c1.email,
c1.title,
c1.first_name,
c1.last_name,
source,
c1.post_code