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法學什麼是 JDBC 中的 CONCUR_UPDATABLE ResultSet？解釋一下？
它是 ResultSet 類的常數，表示可以更新的 ResultSet 物件的併發模式。一般來說，你會將此作為值傳遞給 createStatement() 方法。
Statement createStatement(int resultSetType, int resultSetConcurrency);
具有此併發設定的 ResultSet 是可更新的。也就是說，一旦你獲得一個 ResultSet 物件，就可以更新其內容。
示例
假設我們有一個名為 Employee 的表在資料庫中，其中有以下內容
+----+---------+--------+----------------+ | Id | Name | Salary | Location | +----+---------+--------+----------------+ | 1 | Amit | 3000 | Hyderabad | | 2 | Kalyan | 4000 | Vishakhapatnam | | 3 | Renuka | 6000 | Delhi | | 4 | Archana | 96000 | Mumbai | | 5 | Sumith | 11000 | Hyderabad | | 6 | Rama | 11000 | Goa | | 7 | Mahesh | 5300 | Vishakhapatnam | | 8 | Ramesh | 12000 | Hyderabad | | 9 | Suresh | 7600 | Pune | | 10 | Santosh | 96000 | Mumbai | +----+---------+--------+----------------+
以下示例將員工的薪資值增加 5000 元並列印結果。由於我們在這個示例中建立的 ResultSet 是可更新的，你可以更新它並顯示其值。
import java.sql.*;
public class Updatable {
public static void main(String [] args) throws Exception {
//Registering the Driver
DriverManager.registerDriver(new com.mysql.jdbc.Driver());
//Getting the connection
String mysqlUrl = "jdbc:mysql:///TestDB";
Connection con = DriverManager.getConnection(mysqlUrl, "root", "password");
System.out.println("Connection established......");
//Creating a Statement object
Statement stmt = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_UPDATABLE);
//Retrieving the data
ResultSet rs = stmt.executeQuery("select * from Employees");
//Printing the contents of the table
System.out.println("Contents of the table: ");
rs.beforeFirst();
while(rs.next()) {
System.out.print("ID: " + rs.getInt("id"));
System.out.print(", Salary: " + rs.getInt("Salary"));
System.out.print(", Name: " + rs.getString("Name"));
System.out.println(", Location: " + rs.getString("Location"));
}
System.out.println();
//Moving the pointer to the starting point in the ResultSet
rs.beforeFirst();
//Updating the salary of each employee by 5000
while(rs.next()) {
//Retrieve by column name
int newSal = rs.getInt("Salary") + 5000;
rs.updateInt( "Salary", newSal );
rs.updateRow();
}
System.out.println("Contents of the ResultSet after increasing salaries");
rs.beforeFirst();
while(rs.next()) {
System.out.print("ID: " + rs.getInt("id"));
System.out.print(", Salary: " + rs.getInt("Salary"));
System.out.print(", Name: " + rs.getString("Name"));
System.out.println(", Location: " + rs.getString("Location"));
}
System.out.println();
}
}輸出
Connection established...... Contents of the table: ID: 1, Salary: 3000, Name: Amit, Location: Hyderabad ID: 2, Salary: 4000, Name: Kalyan, Location: Vishakhapatnam ID: 3, Salary: 6000, Name: Renuka, Location: Delhi ID: 4, Salary: 96000, Name: Archana, Location: Mumbai ID: 5, Salary: 11000, Name: Sumith, Location: Hyderabad ID: 6, Salary: 11000, Name: Rama, Location: Goa ID: 7, Salary: 5300, Name: Mahesh, Location: Vishakhapatnam ID: 8, Salary: 12000, Name: Ramesh, Location: Hyderabad ID: 9, Salary: 7600, Name: Suresh, Location: Pune ID: 10, Salary: 96000, Name: Santosh, Location: Mumbai Contents of the ResultSet after increasing salaries ID: 1, Salary: 8000, Name: Amit, Location: Hyderabad ID: 2, Salary: 9000, Name: Kalyan, Location: Vishakhapatnam ID: 3, Salary: 11000, Name: Renuka, Location: Delhi ID: 4, Salary: 101000, Name: Archana, Location: Mumbai ID: 5, Salary: 16000, Name: Sumith, Location: Hyderabad ID: 6, Salary: 16000, Name: Rama, Location: Goa ID: 7, Salary: 10300, Name: Mahesh, Location: Vishakhapatnam ID: 8, Salary: 17000, Name: Ramesh, Location: Hyderabad ID: 9, Salary: 12600, Name: Suresh, Location: Pune ID: 10, Salary: 101000, Name: Santosh, Location: Mumbai
更新於： 2019 年 7 月 30 日
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