Java 和 MySQL - 更新结果集

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ResultSet 接口包含用于更新结果集数据的更新方法的集合。

与 get 方法一样，每种数据类型都有两种更新方法 -

• 一个接受列名的列。

• 接受列索引的一个。

例如，要更新结果集当前行的字符串列，您可以使用以下 updateString() 方法之一 -

java.sql 包中提供了八种基本数据类型以及 String、Object、URL 和 SQL 数据类型的更新方法。

更新结果集中的行会更改 ResultSet 对象中当前行的列，但不会更改基础数据库中的列。要更新对数据库中行的更改，您需要调用以下方法之一。

以下是使用结果集教程中描述的ResultSet.CONCUR_UPDATABLE和ResultSet.TYPE_SCROLL_INSENSITIVE的示例。此示例将解释表上的 INSERT、UPDATE 和 DELETE 操作。

应该注意的是，您正在处理的表应该正确设置主键。让我们首先更新我们的参考表。

删除表并再次创建表Employees ，如下所示 -

mysql> use TUTORIALSPOINT;
mysql> drop table Employees;
Query OK, 0 rows affected (0.08 sec)
mysql> create table Employees
    -> (
    -> id int primary key auto_increment,
    -> age int not null,
    -> first varchar (255),
    -> last varchar (255)
    -> );
Query OK, 0 rows affected (0.08 sec)
mysql>

创建数据记录

最后，您在 Employee 表中创建几条记录，如下所示 -

mysql> INSERT INTO Employees(AGE, FIRST, LAST) VALUES (18, 'Zara', 'Ali');
Query OK, 1 row affected (0.05 sec)

mysql> INSERT INTO Employees(AGE, FIRST, LAST) VALUES (25, 'Mahnaz', 'Fatma');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO Employees(AGE, FIRST, LAST) VALUES (30, 'Zaid', 'Khan');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO Employees(AGE, FIRST, LAST) VALUES (28, 'Sumit', 'Mittal');
Query OK, 1 row affected (0.00 sec)

mysql>

将以下示例复制并粘贴到 TestApplication.java 中，编译并运行如下 -

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class TestApplication {
   static final String DB_URL = "jdbc:mysql://localhost/TUTORIALSPOINT";
   static final String USER = "guest";
   static final String PASS = "guest123";
   static final String QUERY = "SELECT id, first, last, age FROM Employees";

   public static void printResultSet(ResultSet rs) throws SQLException{
      // Ensure we start with first row
      rs.beforeFirst();
      while(rs.next()){
         // Display values
         System.out.print("ID: " + rs.getInt("id"));
         System.out.print(", Age: " + rs.getInt("age"));
         System.out.print(", First: " + rs.getString("first"));
         System.out.println(", Last: " + rs.getString("last"));
      }
      System.out.println();
   }

   public static void main(String[] args) {
      // Open a connection
      try(Connection conn = DriverManager.getConnection(DB_URL, USER, PASS);
         Statement stmt = conn.createStatement(
         ResultSet.TYPE_SCROLL_INSENSITIVE,
         ResultSet.CONCUR_UPDATABLE);
         ResultSet rs = stmt.executeQuery(QUERY);
      ) {		

         System.out.println("List result set for reference....");
         printResultSet(rs);

         // Loop through result set and add 5 in age
         // Move to Before first position so while-loop works properly
         rs.beforeFirst();
         //STEP 7: Extract data from result set
         while(rs.next()){
            // Retrieve by column name
            int newAge = rs.getInt("age") + 5;
            rs.updateDouble( "age", newAge );
            rs.updateRow();
         }
         System.out.println("List result set showing new ages...");
         printResultSet(rs);

         // Insert a record into the table.
         // Move to insert row and add column data with updateXXX()
         System.out.println("Inserting a new record...");
         rs.moveToInsertRow();
         rs.updateString("first","John");
         rs.updateString("last","Paul");
         rs.updateInt("age",40);
         // Commit row
         rs.insertRow();

         System.out.println("List result set showing new set...");
         printResultSet(rs);	

      } catch (SQLException e) {
         e.printStackTrace();
      } 
   }
}

现在让我们按如下方式编译上面的示例 -

C:\>javac TestApplication.java
C:\>

当您运行TestApplication时，它会产生以下结果 -

C:\>java TestApplication
List result set for reference....
ID: 1, Age: 18, First: Zara, Last: Ali
ID: 2, Age: 25, First: Mahnaz, Last: Fatma
ID: 3, Age: 30, First: Zaid, Last: Khan
ID: 4, Age: 28, First: Sumit, Last: Mittal

List result set showing new ages...
ID: 1, Age: 23, First: Zara, Last: Ali
ID: 2, Age: 30, First: Mahnaz, Last: Fatma
ID: 3, Age: 35, First: Zaid, Last: Khan
ID: 4, Age: 33, First: Sumit, Last: Mittal

Inserting a new record...
List result set showing new set...
ID: 1, Age: 23, First: Zara, Last: Ali
ID: 2, Age: 30, First: Mahnaz, Last: Fatma
ID: 3, Age: 35, First: Zaid, Last: Khan
ID: 4, Age: 33, First: Sumit, Last: Mittal
ID: 5, Age: 40, First: John, Last: Paul
C:\>