sql query group by with aggregate - mysql

Question

Have the following table as an example:
zipcode | zipsource | patientcount
-----------------------------------
81501 | CMHSP | 10
81503 | CMHSP | 20
81505 | CMHSP | 30
81501 | SMHRMC | 15
81503 | SMHRMC | 25
81505 | SMHRMC | 35
Trying to show only the zipcodes where the patient count is above 20% of total for Source and Source = SMHRMC(normally a parameter but for the example I've selected SMHRMC). Output table as follows:
zipcode | zipsource | patientcount | Total | Percent
--------------------------------------------------------
81503 | SMHRMC | 25 | 75 | 25%
81505 | SMHRMC | 35 | 75 | 47%
I've tried multiple queries but at this point I don't think I'm close. Any ideas?
The query that works is as follows:
select zipcode,
zip_source,
patient_count,
total_count,
patient_count *100/total_count as percentage
from Zip_Count_Source
cross join (select sum(patient_count) as total_count
from zip_count_Source
where zip_source = 'COMHSP') as X
where zip_source = 'COMHSP' and patient_count*100/total_count > 1
But what I'm having issues with now is that Zip_source can be a multi-value parameter so I change the clauses to zip_source in ('COMHSP', 'SMHRMC') and it works but I want to total_count for each source but not the combined for both sources. Group By did not work after the where clause. Thanks for all that have helped.

Answer 1

Try this:
SELECT zipcode, zipsource, patientcount * 100 / total_count
FROM mytable
CROSS JOIN (SELECT SUM(patientcount) AS total_count
FROM mytable
WHERE zipsource = 'SMHRMC') AS x
WHERE zipsource = 'SMHRMC' AND patientcount / total_count > 0.2
The query uses a CROSS JOIN in order to link the total count of patientcount with the table. Using this count we can calculate the percentage, and filter out any rows not exceeding the desired value.
Demo here

Answer 2

This should do the trick
select t1.zipcode,
t1.zipsource,
t1.patientcount,
t2.total,
t1.patientcount / t2.total * 100 as percent
from yourTable t1
join (
select zipcode, sum(patientcount) as total
from yourTable
group by zipcode
) t2
on t1.zipcode = t2.zipcode
where t1.patientcount / t2.total > 0.2
To filter for a single zipsource, you can add a condition to the where clause
where t1.patientcount / t2.total > 0.2 and
t1.zipsource = 'SMHRMC'

Answer 3

When joining to another table, there is commonly a join condition to filter out rows preventing a Cartesian product (the contents of one table multiplied by another). Since the derived table (total) returns a single value, the join condition is unneeded (the contents of table1 multiplied by 1 = table1).
This is acceptable as long as the value represents what you want to express (i.e., remove the where condition and it will produce the grand total of all patients).
select zipcode,
zipsource,
sum(patientcount) as patientcount,
Total,
concat(round(100*sum_patientcount/Total),'%') as `SHRMC_%`
from table1,
(select count(*) as Total
from table1
where zipsource='SHRMC') as total
where zipsource='SHRMC'
group by zipcode
having sum(patientcount)/total >= .2