Ok. I got the below to run. The formula returns weekly defects / overall production totals. I want to calculate weekly defect / weekly production. Is this possible?

;with totalcount as (

select

cast(count(sn) as decimal) as total

from completedUnit

where MONTH(dateentered) = '10' and operator = 'operator'

)

select

(100 - (cast(count(distinct d.sn) as decimal)/(select * from totalcount))*100) as 'yield'

from productiondefect as d

join completedUnit as c on d.sn = c.sn

where MONTH(c.dateentered) = '10' and c.operator = 'operator'

GROUP BY DATEADD(wk, DATEDIFF(wk, 7, c.dateentered), 7)

ORDER BY DATEADD(wk, DATEDIFF(wk, 7, c.dateentered), 7)