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视图就是任何已命名并保存在数据库中的SELECT查询。因此，视图有时被称为命名查询或存储查询。 物化视图是与普通视图相似的视图 除了一个刷新速度更快的属性。 当主表中发生任何更新时，这些视图会自动更新。
假设主表中发生了任何插入，那么物化视图也会得到更新。在下面的程序中，我们试图展示物化视图是如何工作的。每个数据库软件的实际实现可能不同。
// Java Program to implementat // Materialized view import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.Statement; import java.util.Scanner; import java.sql.PreparedStatement; public class Materialised_View { public static void main(String[] args) { // Declare connection and resultset objects Connection conn; ResultSet rs; // Declare statement objects Statement stmt, stmt1; // query to retrieve the details of student table String query = "select * from student;" ; Scanner sc = new Scanner(System.in); System.out.println( "Student Table is Created as Follows:" ); System.out.println ( "*******Student*********sid sname address---- " ); try { // Register the mysql driver DriverManager.registerDriver( new com.mysql.jdbc.Driver()); // get the connection conn = DriverManager.getConnection // Initialize the statement object stmt = conn.createStatement(); // execute the query and store the result rs = stmt.executeQuery( "select * from student;" ); while (rs.next()) { // Iterate through the result set and display // content of each row of student table. System.out.println(rs.getString( 1 ) + " " + rs.getString( 2 ) + " " + rs.getString( 3 )); } System.out.println( "View of this Student Table is As Follows:" ); rs = stmt.executeQuery( "select * from Student_Data2;" ); System.out.println ( "***********Student View*******sid sname address-------" ); while (rs.next()) { // Iterate through the result set and display // content of view of student table. System.out.println(rs.getString( 1 ) + " " + rs.getString( 2 ) + " " + rs.getString( 3 )); } while ( true ) { // Perform the operations on table System.out.println("Menu:1.Insert2.Delete3. See Changes in View Student_Data24.ExitEnter Choice:"); // take the input from user to insert / delete / see changes int ch = sc.nextInt(); int sid; String sname = "" ; String address = "" ; switch (ch) { case 1 : System.out.println( "Enter sid:" ); sid = sc.nextInt(); System.out.println( "Enter sname:" ); sname = sc.nextLine(); System.out.println( "Enter address:" ); address = sc.nextLine(); // create the preparedStatement object and set the values PreparedStatement st3 = conn.prepareStatement ( "insert into student values(?, ?, ?);" ); st3.setInt( 1 , sid); st3.setString( 2 , sname); st3.setString( 3 , address); st3.executeUpdate(); // create the preparedStatement object and set the values PreparedStatement st1 = conn.prepareStatement ( "insert into Student_Data2 values(?, ?, ?);" ); st1.setInt( 1 , sid); st1.setString( 2 , sname); st1.setString( 3 , address); st1.executeUpdate(); // execute the preparedStatement to insert row System.out.println( "row inserted" ); break ; case 2 : System.out.println( "Enter sid to be deleted:" ); sid = sc.nextInt(); // create the preparedStatement object and set the values PreparedStatement st4 = conn.prepareStatement ( "delete from Student_Data2 where sid=?;" ); st4.setInt( 1 , sid); PreparedStatement st2 = conn.prepareStatement ( "delete from student where sid=?" ); st2.setInt( 1 , sid); // execute the preparedStatement to delete row st2.executeUpdate(); System.out.println( "row deleted" ); break ; case 3 : System.out.println("Changes Done in the Student table also Affects the View Student_Data2"); rs = stmt.executeQuery( "select * from Student_Data2;" ); System.out.println ( "*****Student*******sid sname address--------" ); while (rs.next()) { // Iterate through the result set and display // recent changes of the table // which got reflected in view. System.out.println(rs.getString( 1 ) + " " + rs.getString( 2 ) + " " + rs.getString( 3 )); } break ; case 4 : System.exit( 0 ); // User wants to exit break ; } } } catch (Exception e) { // catch all exceptions here. System.out.println(e); } } } |
输出：
Student Table is Created as Follows: ***********Student************** sid sname address ----------------------------------------------- 131 Rohit Pawar Mumbai 141 Ashish Mane Pune 152 Sagar Gore Mumbai 155 Nitesh Chaure Nagpur 501 Ritesh Dev Chennai 531 Dev Khire Delhi View of this Student Table is As Follows: ***********Student************** sid sname address ----------------------------------------------- 131 Rohit Pawar Mumbai 141 Ashish Mane Pune 152 Sagar Gore Mumbai 155 Nitesh Chaure Nagpur 501 Ritesh Dev Chennai 531 Dev Khire Delhi Menu: 1.Insert 2.Delete 3.See Changes in View Student_Data2 4.Exit Enter Choice:1 Enter sid: 123 Enter sname: Amit Kumar Enter address: Nanded row inserted Menu: 1.Insert 2.Delete 3.See Changes in View Student_Data2 4.Exit Enter Choice:3 Changes Done in the Student table also Affects the View Student_Data2 ***********Student************** sid sname address ----------------------------------------------- 131 Rohit Pawar Mumbai 141 Ashish Mane Pune 152 Sagar Gore Mumbai 155 Nitesh Chaure Nagpur 501 Ritesh Dev Chennai 531 Dev Khire Delhi 123 Amit Kumar Nanded Menu: 1.Insert 2.Delete 3.See Changes in View Student_Data2 4.Exit Enter Choice:2 Enter sid to be deleted: 123 row deleted Menu: 1.Insert 2.Delete 3.See Changes in View Student_Data2 4.Exit Enter Choice:3 Changes Done in the Student table also Affects the View Student_Data2 ***********Student************** sid sname address ----------------------------------------------- 131 Rohit Pawar Mumbai 141 Ashish Mane Pune 152 Sagar Gore Mumbai 155 Nitesh Chaure Nagpur 501 Ritesh Dev Chennai 531 Dev Khire Delhi Menu: 1.Insert 2.Delete 3.See Changes in View Student_Data2 4.Exit Enter Choice:4
说明： 学生表和学生视图在输出开始时打印。然后，如果用户选择选项1在学生表“123 Amit Kumar Nanded”中插入数据，则会将新行插入该表。然后用户选择第三个选项以查看是否在学生视图中反映了更改，选择第三个选项后，我们可以看到相同的条目也被添加到学生视图中。然后用户选择第二个选项，并将sid=123作为输入，从Student表中删除条目。同样，我们可以看到，同样的条目也从Student视图中删除。这就是刷新物化视图的工作方式。
请注意，每个数据库软件的内部实现可能不同。
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