This chapter has described how to combine queries in ways you probably never anticipated. It showed how queries could be chained and placed inside other queries. In addition, it demonstrated how UPDATE can use FROM, and how SELECT can create tables.
Although these features may seem confusing, they are very powerful. In most cases, you will need only the simplest of these features. However, you may get that rare request that requires one of the more complicated queries covered in this chapter. If you recognize such a query, return to this chapter to refresh your memory.