Object DB aggregation query

ObjectDB is an object-oriented Database management system (ODBMS), which supports data storage and query through the object model. Unlike relational Database management system (RDBMS), ObjectDB does not support common aggregate query syntax, such as GROUP BY and aggregate functions (such as SUM, COUNT, AVG, etc.) in SQL. However, similar aggregation queries can be achieved through programming and conditional queries. The following is an example table structure and sample data: **Customer**: - id: Integer - name: String - age: Integer - city: String **Order**: - id: Integer - customerId: Integer - totalAmount: Double - date: Date In this example, Customer represents the customer object and Order represents the order object. Each customer can have multiple orders associated through customerId. Now, we will use the query function of Object DB to demonstrate different types of aggregate queries. 1. Count the number of customers: SELECT COUNT(c) FROM Customer c 2. Calculate the total amount of all orders: SELECT SUM(o.totalAmount) FROM Order o 3. Obtain the highest order amount: SELECT MAX(o.totalAmount) FROM Order o 4. Obtain the minimum order amount: SELECT MIN(o.totalAmount) FROM Order o 5. Calculate the average order amount: SELECT AVG(o.totalAmount) FROM Order o 6. Count order quantity by city: SELECT c.city, COUNT(o) FROM Customer c JOIN c.orders o GROUP BY c.city In this example, we use JOIN to associate the Customer and Order objects, then group them by city and count the number of orders. Please note that these examples are not native aggregate query syntax of Object DB, but are implemented using Object DB's query functionality in conjunction with programming.