Order a Group BY - mysql

Question

There are alot questions on this topic, still can't figure out a way to make this work.
The query I'm doing is:
SELECT `b`.`ads_id` AS `ads_id`,
`b`.`bod_bedrag` AS `bod_bedrag`,
`a`. `ads_naam` AS `ads_naam`,
`a`.`ads_url` AS `ads_url`,
`a`.`ads_prijs` AS `ads_price`,
`i`.`url` AS `img_url`,
`c`.`url` AS `cat_url`
FROM `ads_market_bids` AS `b`
INNER JOIN `ads_market` AS `a`
ON `b`.`ads_id` = `a`.`id`
INNER JOIN `ads_images` AS `i`
ON `b`.`ads_id` = `i`.`ads_id`
INNER JOIN `ads_categories` AS `c`
ON `a`.`cat_id` = `c`.`id`
WHERE `i`.`img_order` = '0'
AND `b`.`u_id` = '285'
GROUP BY `b`.`ads_id`
HAVING MAX(b.bod_bedrag)
ORDER BY `b`.`bod_bedrag` ASC
But, the problem I keep seeing is that I need b.bod_bedrag to be sorted before the GROUP BY is taking place or so. Don't know how to explain it exactly.
The bod_bedrag i'm getting now are the lowest of the bids in the table. I need the highest.
Tried like everything, even tought of not grouping by but using DISTINCT. This didn't work either. Tried order by max, everything I know or could find on the internet.
Image 1 is the situation without the group by. Order By works great (ofc).
Image 2 is with the group by. As you can see, the lowest bid is taken as bod_bedrag. I need the highest.

Answer 1

Judging by your output you want:
SELECT amb.ads_id,
MAX(amb.bod_bedrag) max_bod_bedrag,
am.ads_naam,
am.ads_url,
am.ads_prijs ads_price,
ai.url img_url,
ac.url cat_url
FROM ads_market_bids amb
JOIN ads_images ai
ON ai.ads_id = amb.ads_id
AND ai.img_order = 0
JOIN ads_market am
ON am.id = amb.ads_id
JOIN ads_categories ac
ON ac.id = am.cat_id
WHERE amb.u_id = 285
GROUP BY amb.ads_id,
am.ads_naam,
am.ads_url,
am.ads_prijs,
ai.url,
ac.url
ORDER BY max_bod_bedrag ASC
I have also removed all the unecessary backtickery and aliasing of columns to the same name.
Your HAVING was doing nothing as all the groups 'have' a MAX(amb.bod_rag).

Answer 2

select distinct `b`.`ads_id` as `ads_id`, max(`b`.`bod_bedrag`) as `bod_bedrag`,
`a`.`ads_naam` as `ads_naam`, `a`.`ads_url` as `ads_url`, `a`.`ads_prijs` as `ads_price`,
`i`.`url` as `img_url`, `c`.`url` as `cat_url`
from `ads_market_bids` as `b`
inner join `ads_market` as `a` on `b`.`ads_id` = `a`.`id`
inner join `ads_images` as `i` on `b`.`ads_id` = `i`.`ads_id`
inner join `ads_categories` as `c` on `a`.`cat_id` = `c`.`id`
where `i`.`img_order` = '0' and `b`.`u_id` = '285'
group by b.ads_id, a.ads_naam, a.ads_url, a.ads_prijs, i.url, c.url

Answer 3

One approach is to simulate row_number() (which MySQL does not have), but it allows for selection - by record - rather than by aggregates which may come from disparate source records. It works by adding to variables to each row (it does not increase the number of rows) Then, using an ordered subquery those variables are set to 1 for the highest b.bod_bedrag for each b.ads_id, all other rows perb.ads_id` get a higher RN value. At the end we filter where RN = 1 (which equates the the record containing the highest bid value)
SELECT *
FROM (
SELECT
#row_num :=IF(#prev_value=`b`.`ads_id`, #row_num + 1, 1) AS RN
,`b`.`ads_id` AS `ads_id`
,`b`.`bod_bedrag` AS `bod_bedrag`
,`a`.`ads_naam` AS `ads_naam`
,`a`.`ads_url` AS `ads_url`
,`a`.`ads_prijs` AS `ads_price`
,`i`.`url` AS `img_url`
,`c`.`url` AS `cat_url`
, #prev_value := `b`.`bod_bedrag`
FROM `ads_market_bids` AS `b`
INNER JOIN `ads_market` AS `a` ON `b`.`ads_id` = `a`.`id`
INNER JOIN `ads_images` AS `i` ON `b`.`ads_id` = `i`.`ads_id`
INNER JOIN `ads_categories` AS `c` ON `a`.`cat_id` = `c`.`id`
CROSS JOIN
( SELECT #row_num :=1
, #prev_value :=''
) vars
WHERE `i`.`img_order` = '0'
AND `b`.`u_id` = '285'
ORDER BY `b`.`ads_id`, b`.`bod_bedrag` DESC
)
WHERE RN = 1;
You can even turn off that silly GROUP BY extension, details in the man page:
MySQL Extensions to GROUP BY