2 different AVG column in 1 table with select - mysql

Question

I am trying to make an table that shows an AVG of pickpockets in district with markets and an AVG of pickpockets in districts without Market.
i would like to have the output like this:
district with market | district without market
----------------------------------------------
269 | 34
but instead i get this:
district with market | district without market
----------------------------------------------
269 | 269
34 | 34
this is the query i used:
select round(avg(average),0) as districts_with_markets, round(avg(average),0) as districts_without_markets
from zakkenrollerij
where wijk in (select district
from market)
union
select round(avg(average),0) as districts_with_markets, round(avg(average),0) as districts_without_markets
from zakkenrollerij
where wijk not in (select district
from market)
I hope someone can help me :D

Answer 1

Assuming that distict is unique in market, then you can do this with a left join and conditional aggregation:
select round(avg(case when m.district is not null then average end), 0) as districts_with_markets,
round(avg(case when m.district is null then average end), 0) as districts_without_markets
from zakkenrollerij z left join
market m
on m.district = z.wijk;
If this is not the case, then use a subquery and a flag:
select round(avg(case when hasMarketFlag then average end), 0) as districts_with_markets,
round(avg(case when not hasMarketFlag then average end), 0) as districts_without_markets
from (select z.*,
(exists (select 1
from market m
where m.district = z.wijk
)
) as hasMarketFlag
from zakkenrollerij z;

Answer 2

Try this:-
Select sum(dist_with_markets) as district_with_markets,
sum(dist_without_markets) as district_without_markets
from
(
select round(avg(average),0) as dist_with_markets, 0 as dist_without_markets
from zakkenrollerij
where wijk in (select district
from market)
union
select 0 as dist_with_markets, round(avg(average),0) as dist_without_markets
from zakkenrollerij
where wijk not in (select district
from market) ) a;
Hope this helps:-)

Answer 3

Please try the following...
SELECT ROUND( AVG( with_markets ) ) AS districts_with_markets,
ROUND( AVG( without_markets ) ) AS without_markets
FROM ( SELECT average AS with_markets
NULL AS without_markets
FROM zakkenrollerij
WHERE wijk IN ( SELECT district
FROM market )
UNION
SELECT NULL,
average
FROM zakkenrollerij
WHERE wijk NOT IN ( SELECT district
FROM market )
) AS tempTable;
This starts by forming a list of all the values of average within zakkenrollerij that qualify as within. No attempt to perform calculations is made at this stage. The second column is for those values that qualify as without - all of its values will be set to NULL at this stage.
This list is then joined vertically with its without counterpart using the UNION operator.
The joined list then has the ROUND( AVG() ) operations performed upon its columns.
If you have any questions or comments, then please feel free to post a Comment accordingly.

Answer 4

You are now going trough the table twice, selecting the same variable twice under different names:
round(avg(average),0) as districts_with_markets, round(avg(average),0) as districts_without_market
Instead of uniting the tables afterwards you can use CASE to select a variable with specific conditions. This should give the wanted result:
select round(avg(case when wijk in (select district from market) then average else null end),0) as districts_with_markets,
round(avg(case when wijk not in (select district from market) then average else null end),0) as districts_without_markets
from zakkenrollerij