Querying a large table using mysql - mysql

Question

I manage a property website. I have a table with banned users (small table) and a table called advert_views which keeps track of each listing that each user views (currently 1.3m lines and growing). The advert_views table alsio takes note of the IP address for every advert viewed).
I want to get the IP addresses used by the banned users and check if any of these banned users have opened new accounts. I ran the following query:
SELECT adviews.user_id AS 'banned user_id',
adviews.client_ip AS 'IPs used by banned users',
adviews2.user_id AS 'banned users that opened a new account'
FROM banned_users
LEFT JOIN users on users.email_address = banned_users.email_address #since I don't store the user_id in banned_users
LEFT JOIN advert_views adviews ON adviews.user_id = users.id AND adviews.user_id IS NOT NULL # users may view listings when not logged in but they have restricted access to the information on the listing
LEFT JOIN (SELECT client_ip,
user_id
FROM advert_views
WHERE user_id IS NOT NULL
) adviews2
ON adviews2.client_ip = adviews.client_ip
WHERE banned_users.rec_status = 1 and adviews.user_id <> adviews2.user_id
GROUP BY adviews2.user_id
I applied an index on the advert_views table and the users table as per below:
enter image description here
My query takes half an hour to execute. Is there a way how to improve my query speed?
Thanks!
Chris

Answer 1

First of all: Why do you outer join the tables? Or better: Why do you try to outer join the tables? A left join is meant to get data from a table even when there is no match. But then your results could contain rows with all values null. (That doesn't happen though, because adviews.user_id <> adviews2.user_id in your where clause dismisses all outer-joined rows.) Don't give the DBMS more work to do than necessary. If you want inner joins, then don't outer join. (Though the difference in execution time won't be huge.)
Next: You select from banned_users, but you only use it to check existence. You shouldn't do this. Use an EXISTS or IN clause instead. (This is mainly for readability and in order not to produce duplicate results. This probably won't speed things up.)
SELECT av1.user_id AS 'banned user_id',
av2.client_ip AS 'IPs used by banned users',
av2.user_id AS 'banned users that opened a new account'
FROM adviews av1
JOIN adviews av2 ON av2.client_ip = av1.client_ip AND av2.user_id <> av1.user_id
WHERE av1.user_id IN
(
SELECT user_id
FROM users
WHERE email_address IN (select email_address from banned_users where rec_status = 1)
)
GROUP BY av2.user_id;
You may replace the inner IN clause with a join. It's mostly a matter of personal preference, but it is also that in the past MySQL sometimes didn't perform well on IN clauses, so many people made it a habit to join instead.
WHERE av1.user_id IN
(
SELECT u.user_id
FROM users u
JOIN banned_users bu ON bu.email_address = u.email_address
WHERE bu.rec_status = 1
)
At last consider removing the GROUP BY clause. It reduces your results to one row per reusing user_id, showing one of its related banned user_ids (arbitrarily chosen in case there is more than one). I don't know your tables. Are you getting many records per reusing user_id? If not, remove the clause.
As to indexes I suggest:
banned_users(rec_status, email_address)
users(email_address, user_id)
adviews(user_id, client_ip)
adviews(client_ip, user_id)