This is a sample of some basic SQL exercises I completed in an hour.
KKennedy_Data_Science_Product_Analytics_exercise.pdf is a complete version of the created and formatted document I created, along with the answers to the SQL exercises. The original document containing the initial questions and formatting is available in Data_Science_Product_Analytics_exercise.pdf.
I have more tricks available in the wiki-code repository, and also a lovelly SQL Tricks Gitbook, available here.