MySQL 5.7 | GROUP BY | Non Aggregated Column Error - mysql

Question

I upgraded our mysql db from 5.6 to 5.7 and am in the process of fixing some queries which are throwing some errors. One of the queries I am working involves a GROUP BY with a COALESCE.
Here is the query (abstracted) that works:
SELECT
MAX(a.id),
a.entered,
count(*) AS teh_count
FROM
a
INNER JOIN
b ON b.id = a.link_to_b_id
INNER JOIN
c ON c.link_to_b_id = b.id
WHERE
b.revision_id > 0
AND
c.terminated_at = '0000-00-00 00:00:00'
AND
a.created_at > date_sub(NOW(), INTERVAL 8 HOUR)
GROUP BY
a.entered
ORDER BY
teh_count DESC
LIMIT
6;
But I need to COALESCE a.entered with c.override, so I tried the following:
SELECT
MAX(a.id),
a.entered,
COALESCE(c.override, a.entered) AS appearance,
count(*) AS teh_count
FROM
a
INNER JOIN
b ON b.id = a.link_to_b_id
INNER JOIN
c ON c.link_link_to_b_id = b.id
WHERE
b.revision_id > 0
AND
c.terminated_at = '0000-00-00 00:00:00'
AND
a.created_at > date_sub(NOW(), INTERVAL 8 HOUR)
GROUP BY
a.entered
ORDER BY
teh_count DESC
LIMIT
6;
But MySQL 5.7 now throws the following error: Expression #2 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'st_core.tuc.code_appearance_override' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by
I assume I can can change the sql_mode, but I'd prefer not too. What the error is telling me makes sense, in that the COALESCE column is not aggregated, so as a test I wrapped it with MAX and it works, however it seems kind of hacky to me.
Is there a more elegant solution?

Answer 1

You should also include a.entered in your group by clause and that's what the error saying. Though not sure why you are grouping by an different column a.code_entered?
Your query should look like
SELECT
MAX(a.id),
a.entered,
COALESCE(c.override, a.entered) AS appearance,
count(*) AS teh_count
FROM
a
INNER JOIN
b ON b.id = a.link_to_b_id
INNER JOIN
c ON c.link_link_to_b_id = b.id
WHERE
b.revision_id > 0
AND
c.terminated_at = '0000-00-00 00:00:00'
AND
a.created_at > date_sub(NOW(), INTERVAL 8 HOUR)
GROUP BY
a.entered,
COALESCE(c.override, a.entered)
ORDER BY
teh_count DESC
LIMIT
6;

Answer 2

I think you intend something like this:
SELECT MAX(a.id),
COALESCE(c.override, a.entered) AS appearance,
count(*) AS the_count
FROM a INNER JOIN
b
ON b.id = a.link_to_b_id INNER JOIN
c
ON c.link_link_to_b_id = b.id
WHERE b.revision_id > 0 AND
c.terminated_at = '0000-00-00 00:00:00' AND
a.created_at > date_sub(NOW(), INTERVAL 8 HOUR)
GROUP BY appearance
ORDER BY the_count DESC
LIMIT 6;
This removes a.entered from the SELECT list so there is only one column for grouping. That column can be referenced by table alias in the GROUP BY.