需要使用复合主键计数不同的值

I have to generate a report that displays the name of different locations and the number of times unique course offerings are offered in these locations. The report needs to only indicate the city and the no. of unique course offerings and be sorted by the highest number of unique offerings. The problem I have is the offering table has a composite primary key (offering begin date and course code)I have to generate a report that displays the n