在mysql中以最新日期加入行

Question

i'm new to mysql and have been tryn to make this work without any luck. i am joining 3 tables and i am tryn to join third table with the row with most recent record as per date. here is my mysql query

SELECT mg.region_name, mu.contact_person, 
    mu.contact_number, mu.status, mu.company_name, mu.user_type, MAX(mf.follow_up_date), mf.date, mu.user_id
FROM p1006_marketing_group as mg 
JOIN p1006_marketing_users as mu ON mg.id = mu.region_id 
JOIN ( SELECT user_id_fk,MAX(follow_up_date) 
        FROM p1006_marketing_follow_up ) as mf 
    ON mu.user_id = mf.user_id_fk 
    WHERE mu.user_id_done = "" AND ( mg.id = 3 OR mg.id = 7 OR mg.id = 6 ) 
GROUP BY mf.user_id_fk

i get the following error

Unknown column 'mf.follow_up_date' in 'field list'

i am really confused because i do have to column follow_up_date.

i would be really greateful for any help possible

Answer 1

You've forgotten to give your MAX(follow_up_date) inside your subquery, an alias

Edit your query so it looks like:

MAX(follow_up_date) as follow_up_date

Please also note, your query has other issues, such as the select list containing about 8 columns that are not part of an aggregate function, but your group by lists only one column. While this might work in MySQL because it can (if configured so) fill in missing group by columns for you, you should really get into the habit of specifying them, to avoid future issues in other employment that uses different database systems

Answer 2

You are missing alias for MAX column.

SELECT 
  mg.region_name, mu.contact_person, mu.contact_number, mu.status, 
  mu.company_name, mu.user_type, MAX(mf.follow_up_date), mf.date, mu.user_id

FROM p1006_marketing_group as mg 
JOIN p1006_marketing_users as mu ON mg.id = mu.region_id 
JOIN ( SELECT user_id_fk,MAX(follow_up_date) 'follow_up_date' FROM p1006_marketing_follow_up ) as mf ON mu.user_id = mf.user_id_fk 
WHERE mu.user_id_done = "" AND ( mg.id = 3 OR mg.id = 7 OR mg.id = 6 ) 
GROUP BY mf.user_id_fk