Welcome to ssc. There's an excellent article linked in my signature block "please read this" - have a read, it will help you get faster, more accurate answers to your questions.
What's the relationship between the two tables?
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden