How to combine multiple zipcode polygons into one polygon

In CartoDB, we have a table of chapters that make up a national organization. Each chapter record has a polygon that defines the geographical area that the chapter covers. The area a chapter covers is defined by zipcodes and which zipcodes are included in a chapter can change over time. I understand that CartoDB has a table with polygon information for US zipcodes. Given a zipcode to chapter table that I can produce, I'd like to create a fairly simple process to redefine the chapter polygons using the CartoDB zipcode/polygon table. I have the following specific questions but any help toward achieving the state goal would be greatly appreciated.

1. What is the zip/polygon table name and how do I reference it in queries?


2. What's the best way to use my zip to chapter mapping table and the CartoDB zip/polygon table to create a single polygon for each chapter?