php - WHERE clause with inner join -

I have the following questions to calculate the amount of devices in my database. I just try to add a "WHERE" clause to select the device and select the device I count with the name "iphone", select the device (*), count as count (*), Device with total AS percentage (device) = device where device = 'apple' cross join (total number of devices from selection number (*)) x group b1

Tried, but they all got results in a mysql error. What is the correct position of WHERE clause?

where arrives after FROM and earlier GROUP BY