SQL

The intention here is to describe ANSI SQL, rather than vendor specific SQL.

Joins

A good visual starting point is Visual Representation of SQL Joins - CodeProject

Where Clause

It is easy to forget how "BETWEEN" works, so, for clarity it is this:

WHERE Length BETWEEN 5 AND 10
WHERE Length >= 5 AND Length <= 10
It is also worth noting that BETWEEN works with "WHERE" and "HAVING".