mysql - rewrite query with subqueries - mysql

Question

Consider a table Users with columns Id, Name, Surname and a table Actions with columns Ip and Actor. I need to retrieve, for every Ip, the set of users who did as action using that Ip.
What I have now looks like:
SELECT a.ip, (
SELECT GROUP_CONCAT(t.id, '-', t.name, ' ', t.surname) FROM(
SELECT ud.id, ud.name, ud.surname
FROM users_data AS ud
JOIN actions AS a2 ON a2.actor = ud.id
WHERE a2.ip = a.ip
GROUP BY ud.id) AS t
)
FROM actions AS a
WHERE a.ip != '' AND a.ip != '0.0.0.0'
GROUP BY a.ip
It doesn't work because a.ip is unknown in the where clause in the inner subquery.
Do to performance issues, I need to avoid to use DISTINCT.
Any suggestion?

Answer 1

You can rewrite your query as
SELECT n.ip, GROUP_CONCAT( DISTINCT n.your_user SEPARATOR ' -- ') `users` FROM
(
SELECT a.ip AS ip, CONCAT(t.id, '-', t.name, ' ', t.surname) `your_user`
FROM users_data AS ud
JOIN actions AS a ON a.actor = ud.id
) `new_table` n
WHERE n.ip != '' AND n.ip != '0.0.0.0'
GROUP BY n.ip
Note Be aware of that the result is truncated to the maximum length
that is given by the group_concat_max_len system variable, which
has a default value of 1024

Answer 2

have you tried writing the condition a2.ip = a.ip outside the subquery.?
i.e. in the where clause of outer query!

Answer 3

I solved it using this query (still quite slow, so there's still space for improvements...):
SELECT SQL_NO_CACHE t.ip, COUNT(t.id) AS c, GROUP_CONCAT(t.id, '-', t.name, ' ', t.surname, '-', t.designerAt > 0) FROM (
SELECT a.ip, ud.id, ud.name, ud.surname, u.designerAt
FROM actions AS a
JOIN users_data AS ud ON ud.id = a.actor
JOIN users AS u ON u.id = a.actor
WHERE a.ip != ''
AND a.ip != '0.0.0.0'
AND a.actor !=0
GROUP BY a.ip, a.actor
) AS t
GROUP BY t.ip