What ensures the execution of queries to the database?

The database management system (DBMS) along with drivers and APIs that allow an application to interact with the database ensures query execution.

In Java, JDBC (Java Database Connectivity) is often used for this purpose — a standard API for connecting to and executing SQL queries on various databases.

Example of simple query execution via JDBC:

import java.sql.*;

public class DbExample {
    public static void main(String[] args) throws SQLException {
        String url = "jdbc:mysql://localhost:3306/mydb";
        String user = "root";
        String password = "password";

        Connection conn = DriverManager.getConnection(url, user, password);
        Statement stmt = conn.createStatement();
        ResultSet rs = stmt.executeQuery("SELECT * FROM users");

        while (rs.next()) {
            System.out.println("User: " + rs.getString("username"));
        }

        rs.close();
        stmt.close();
        conn.close();
    }
}

Thus, query execution is provided by the interaction of the application with the DBMS through the appropriate drivers and APIs.