How can I use outer join with subquery and groupby? - database

Question

Tool : MySQL Workbench 6.3
Version : MySQL 5.7
SELECT *
FROM cars as a, battery_log as b
WHERE a.user_seq = 226 AND a.seq = b.car_seq
AND b.created = ( SELECT MAX(created) FROM battery_log WHERE car_seq = a.seq )
GROUP BY car_type
ORDER BY a.created DESC;
I want to turn this query into an outer join.
By searching user_seq in the'cars' table
I need to get the latest value of the battery log in the one-to-many relationship of the corresponding car table.
Sometimes the battery log does not have a value that matches car seq, so it is truncated from the joining process of table a and table b. How can I fix this?
SELECT a.*, b.battery
FROM cars as a
LEFT OUTER JOIN battery_log as b ON a.seq = b.car_seq
LEFT OUTER JOIN ( SELECT MAX(created) FROM battery_log WHERE a.seq = b.car_seq) as c
ON b.created = c.MAX(created)
WHERE a.user_seq = 226
GROUP BY car_type
ORDER BY a.created DESC
I tried to fix it this way, but I got the following error:
Error Code: 1054, Unknown column'a.seq' in'where clause'

Answer 1

I solved this problem like this.
SELECT *
FROM cars as a
LEFT OUTER JOIN battery_log as b ON a.seq = b.car_seq
AND b.created = (SELECT MAX(created) FROM battery_log WHERE car_seq = b.car_seq)
WHERE a.user_seq = 226
GROUP BY car_type
ORDER BY a.created DESC;
After LEFT OUTER JOIN ... ON, an additional condition was given with AND, and the query was performed according to the condition.