ค้นหาราคาต่อหน่วยเฉลี่ยของเพลงแจ๊ส ไม่จำเป็นต้องใช้ตารางทั้งหมด
Find the average unit price of jazz tracks.It is not neccessary to use all the tables.
 employee:  employeeid [ number]  lastname [ text]  firstname [ text]  title [ text]  reportsto [ number]  birthdate [ time]  hiredate [ time]  address [ text]  city [ text]  state [ text]  country [ text]  postalcode [ text]  phone [ text]  fax [ text]  email [ text] 
SELECT AVG(unitprice) FROM genre AS T1 JOIN track AS T2 ON T1.genreid = T2.genreid WHERE T1.name = "Jazz"