Given a bookstore database schema, write SQL queries using joins and aggregations to answer questions about sales, inventory, and customer data.

Focus on demonstrating your understanding of SQL joins and aggregations by clearly articulating the relationships between the tables in the bookstore database schema. Start by identifying the key tables involved, such as sales, inventory, and customers, and explain how they relate to each other. When writing your queries, ensure you use appropriate join types (INNER, LEFT, etc.) based on the data you need to retrieve. Additionally, incorporate aggregate functions like COUNT, SUM, or AVG to derive meaningful insights from the data. Be prepared to explain your thought process and the rationale behind your query structure, as clarity in your approach is crucial.