Group by inside inner join 1055 - mysql

Question

So, i have 2 tables one of them is a control list of holidays (1 for holiday and 0 for not holiday) and the day of the week on that date it kinda looks like this:
calendar_date
Day_of_week
Holiday_flg
2016-01-02
Monday
1
2016-02-03
Friday
0
2016-02-01
Monday
1
And a second table with some restaurant info that looks like this:
Visit date: refers to the day the visitors arrive at the restaurant
Reserve visitors: refers to the day the visitors created a reservation on the restaurant (not used in this problem, just part of the main table)
ID
Visit_date
reserve_datetime
reserve_visitors
1023044
2016-02-01
2016-01-01
5
1041331
2016-01-01
2016-01-01
2
1023044
2016-01-01
2016-01-01
4
I used this query to join both tables together by date
SELECT * from restaurants_visitors
inner join date_info
on restaurants_visitors.visit_date= date_info.calendar_date
where holiday_flg=1
limit 10
;
which returns both tables joined by the date
I want to group them by restaurant ID, so i can get the highest average number of vistors on holidays, and the percentage of growth of the amount of visitors week over week for the last 4 weeks
So far i have tried something like this
SELECT * FROM restaurants_visitors as rv
inner join date_info as df
on rv.visit_date= df.calendar_date
where df.holiday_flg=1
group by rv.id
limit 10
;
But i keep getting this error code:
Error Code: 1055. Expression #2 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'database.restaurants_visitors.visit_date' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by 0.024 sec
Expected Output
List of top 5 more visited restaurants in holidays( Table with id of restaurant and avg visitors on holidays)in dsc order
ID
Average_visitorsin_holidays
1023044
4.5
1041331
2
List of percentage of growth of the amount of visitors week over week for the last four weeks of the data?(Table with percentage of growth over weeks)
week
percentage of growth over last week
4
unknow result
3
unknow result
Which day of the week there are usually more visitors on average in restaurants.
(single row with day of the week with more visitors)
Day of the week
AVG visitor per day of week
Monday
4.5
1041331
1

Answer 1

Ok, the main problem is that you're selecting ALL the columns but only defining rv.id as the group identifier.
You want to start with something like this:
SELECT
rv.id,
df.calendar_date,
sum(rv.reserve_visitors) as total_visitors
FROM
restaurants_visitors as rv
inner join
date_info as df on rv.visit_date= df.calendar_date
WHERE
df.holiday_flg=1
GROUP BY
rv.id,
df.calendar_date
This will tell you the total visitors per restaurant per holiday. With that in hand, we can find the average visitors per restaurant on holidays:
WITH
holiday_visitors as (
SELECT
rv.id,
df.calendar_date,
sum(rv.reserve_visitors) as total_visitors
FROM
restaurants_visitors as rv
inner join
date_info as df on rv.visit_date= df.calendar_date
WHERE
df.holiday_flg=1
GROUP BY
rv.id,
df.calendar_date
)
SELECT
id,
avg(total_visitors) as avg_holiday_visitors
FROM
holiday_visitors
GROUP BY
id
ORDER BY
avg_holiday_visitors desc
This will tell you which restaurants had the most traffic on average on holidays. How you limit it to the top 5 depends on the database you are using.