MySQL: Error 1055 When attempting to Return Count of Referrer by Month in Year 2020

I'm getting the following error code:

Error Code: 1055. Expression #1 of ORDER BY clause is not in GROUP BY clause and contains nonaggregated column 'usergrowthhomework.weblogs.day' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

This code is a result of me attempting to run the following query, which is supposed to return the number of times a 'referrer' appears each month in the year 2020:

SELECT MONTH(day) MONTH, referrer, COUNT(referrer) AS cumulative_pageviews
FROM weblogs
WHERE YEAR(day) >= '2020'
GROUP BY MONTH(day), referrer
ORDER BY day, referrer;

My table's columns look like this:

user_no - int name - varchar(200) referrer - varchar(200) start_date - timestamp day - date

Can anyone explain why I'm getting such an error? I clearly included all appropriate expressions in the GROUP BY and SELECT clauses.

I'm using the MySQL workbench to run this query.

Solution

As the error suggests, the day column in the order by clause isn't in the group by clause, and thus can't be used there. You should order by MONTH(day) instead:

SELECT   MONTH(day) MONTH, referrer, COUNT(referrer) AS cumulative_pageviews
FROM     weblogs
WHERE    YEAR(day) >= 2020
GROUP BY MONTH(day), referrer
ORDER BY MONTH(day), referrer;
-- Here -^