Using Java to Implement Versant Object Database Aggregation Queries
To implement aggregate queries in Versant Object Database using Java, it is necessary to introduce the corresponding Java SDK and related libraries for Versant Object Database, as well as understand the basic concepts and APIs of Versant Object Database.
The following are examples of using Java to implement several aggregated queries in Versant Object Database:
1. Statistical quantity:
import com.versant.fund.FundQuery;
import com.versant.fund.FundQueryResult;
import com.versant.fund.FundScalarInt;
public class CountQueryExample {
public static void main(String[] args) {
String query = "SELECT COUNT(*) FROM Person";
FundQueryResult result = FundQuery.execute(query);
int count = ((FundScalarInt) result.next()).value;
System.out.println("Count: " + count);
}
}
Maven coordinates:
<dependency>
<groupId>com.versant</groupId>
<artifactId>versant-sdk</artifactId>
<version>10.0.0</version>
</dependency>
2. Sum:
import com.versant.fund.FundQuery;
import com.versant.fund.FundQueryResult;
import com.versant.fund.FundScalarDouble;
public class SumQueryExample {
public static void main(String[] args) {
String query = "SELECT SUM(salary) FROM Employee";
FundQueryResult result = FundQuery.execute(query);
double sum = ((FundScalarDouble) result.next()).value;
System.out.println("Sum: " + sum);
}
}
3. Average value:
import com.versant.fund.FundQuery;
import com.versant.fund.FundQueryResult;
import com.versant.fund.FundScalarDouble;
public class AvgQueryExample {
public static void main(String[] args) {
String query = "SELECT AVG(age) FROM Person";
FundQueryResult result = FundQuery.execute(query);
double avg = ((FundScalarDouble) result.next()).value;
System.out.println("Average: " + avg);
}
}
4. Maximum and minimum values:
import com.versant.fund.FundQuery;
import com.versant.fund.FundQueryResult;
import com.versant.fund.FundScalarInt;
public class MinMaxQueryExample {
public static void main(String[] args) {
String query = "SELECT MIN(salary), MAX(salary) FROM Employee";
FundQueryResult result = FundQuery.execute(query);
FundScalarInt min = (FundScalarInt) result.next();
FundScalarInt max = (FundScalarInt) result.next();
System.out.println("Min: " + min.value);
System.out.println("Max: " + max.value);
}
}
These sample codes can be used to perform aggregate queries through the Java SDK of Versant Object Database. Among them, aggregation functions include COUNT, SUM, AVG, MIN, MAX, which can be called using query statements similar to SQL syntax.
Please note that the specific code implementation may vary depending on the version of Versant Object Database and the usage of the SDK. The above example applies to Versant Object Database version 10.0.0. In practical use, please refer to official documents and relevant APIs for development.
