Get minimum from result with GROUP BY in MySQL - mysql

Question

I have table it store hierarchy data in MySQL this table store stable relation but if each user less than 1000 buy removed and user User a lower level replace this is my code and work fine, after GROUP BY it contain all ancestor of descendant with compare then COUNT(*) AS level count level each user. This I have SQL code to compress data According to minimum buy for each user
+-------------+---------------+-------------+
| ancestor_id | descendant_id | path_length |
+-------------+---------------+-------------+
| 1 | 1 | 0 |
| 1 | 2 | 1 |
| 1 | 3 | 1 |
| 1 | 4 | 2 |
| 1 | 5 | 3 |
| 1 | 6 | 4 |
| 2 | 2 | 0 |
| 2 | 4 | 1 |
| 2 | 5 | 2 |
| 2 | 6 | 3 |
| 3 | 3 | 0 |
| 4 | 4 | 0 |
| 4 | 5 | 1 |
| 4 | 6 | 2 |
| 5 | 5 | 0 |
| 5 | 6 | 1 |
| 6 | 6 | 0 |
+-------------+---------------+-------------+
This is table buy
+--------+--------+
| userid | amount |
+--------+--------+
| 2 | 2000 |
| 4 | 6000 |
| 6 | 7000 |
| 1 | 7000 |
SQL code
SELECT a.*
FROM
( SELECT userid
FROM webineh_user_buys
GROUP BY userid
HAVING SUM(amount) >= 1000
) AS buys_d
JOIN
webineh_prefix_nodes_paths AS a
ON a.descendant_id = buys_d.userid
JOIN
(
SELECT userid
FROM webineh_user_buys
GROUP BY userid
HAVING SUM(amount) >= 1000
) AS buys_a on (a.ancestor_id = buys_a.userid )
JOIN
( SELECT descendant_id
, MAX(path_length) path_length
FROM webineh_prefix_nodes_paths
where a.ancestor_id = ancestor_id
GROUP
BY descendant_id
) b
ON b.descendant_id = a.descendant_id
AND b.path_length = a.path_length
GROUP BY a.descendant_id, a.ancestor_id
I need get max path_length where ancestor_id have At least 1000 amount buy but have error in where in subquery where a.ancestor_id = ancestor_id error code
1054 - Unknown column 'a.ancestor_id' in 'where clause'
I add SQLFidle demo.

Answer 1

You could use this query:
select m.userid as descendant,
p.ancestor_id,
p.path_length
from (
select b1.userid,
min(case when b2.amount >= 1000
then p.path_length
end) as path_length
from (select userid, sum(amount) amount
from webineh_user_buys
group by userid
having sum(amount) >= 1000
) as b1
left join webineh_prefix_nodes_paths p
on p.descendant_id = b1.userid
and p.path_length > 0
left join (select userid, sum(amount) amount
from webineh_user_buys
group by userid) as b2
on p.ancestor_id = b2.userid
group by b1.userid
) as m
left join webineh_prefix_nodes_paths p
on p.descendant_id = m.userid
and p.path_length = m.path_length
order by m.userid
Output for sample data in the question:
| userid | ancestor_id | path_length |
|--------|-------------|-------------|
| 1 | (null) | (null) |
| 2 | 1 | 1 |
| 4 | 2 | 1 |
| 6 | 4 | 2 |
SQL fiddle