Pasted

select year, count(id_patient) as under_8_weeks, sum(positive) from (select year(date_blood_taken) as year, id_patient, 
if(pcr_result=1,1,0) as positive 
from testing_specimen where
which_pcr=1 and 
timestampdiff(week,date_of_birth,date_blood_taken)<=8 and date_blood_taken
between '2015-01-01' and '2017-06-30'
group by id_patient
)d
group by year