ค้นหาจำนวนผลิตภัณฑ์ต่างๆ ที่ผลิตโดยบริษัทในเมืองสำนักงานใหญ่ต่างๆ ไม่จำเป็นต้องใช้ตารางทั้งหมด
Find the number of different products that are produced by companies at different headquarter cities.It is not neccessary to use all the tables.
 manufacturers:  code [ number]  name [ text]  headquarter [ text]  founder [ text]  revenue [ number] 
SELECT COUNT(DISTINCT T1.name), T2.headquarter FROM products AS T1 JOIN manufacturers AS T2 ON T1.manufacturer = T2.code GROUP BY T2.headquarter