Final answer:
External databases in a data warehouse include competitor data, stock market data, and mailing lists, offering complementary insights alongside internal data sources.
Step-by-step explanation:
In the context of a data warehouse, external databases refer to data sources that are outside the organization's internal systems. Examples of these external databases include competitor data, stock market data, and mailing lists. These sources provide additional insights that complement internal data such as marketing, sales, accounting, and inventory data, which are all typically internal to an organization. Thus, the external databases in the list provided are:
- Competitor data
- Stock market data
- Mailing lists