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法律研究JDBC 中的 CONCUR_READ_ONLY ResultSet 是什么？解释一下？
通常情况下，你可以将此值作为 ResultSet Concurrency 类型的 createStatement() 方法的值传递。
Statement createStatement(int resultSetType, int resultSetConcurrency)
此类型结果集不可更新。即，一旦获取了 ResultSet 对象，就无法更新其内容。
示例
假设我们在数据库中有一张名为 Employee 的表，其中包含如下内容
+----+---------+--------+----------------+ | 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 | +----+---------+--------+----------------+
在以下示例中，我们尝试将员工的薪水值增加 5000，并打印结果。
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://127.0.0.1/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_READ_ONLY);
//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("Conetnets of the resultset after increaing 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();
}
}错误
由于我们创建的 ResultSet 是只读的，因此无法更新 ResultSet 的内容，并且会收到以下错误。
Connection established...... Contents of the table: 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 Exception in thread "main" com.mysql.jdbc.NotUpdatable: Result Set not updatable.This result set must come from a statement that was created with a result set type of ResultSet.CONCUR_UPDATABLE, the query must select only one table, can not use functions and must select all primary keys from that table. See the JDBC 2.1 API Specification, section 5.6 for more details.This result set must come from a statement that was created with a result set type of ResultSet.CONCUR_UPDATABLE, the query must select only one table, can not use functions and must select all primary keys from that table. See the JDBC 2.1 API Specification, section 5.6 for more details. at com.mysql.jdbc.ResultSetImpl.updateInt(ResultSetImpl.java:8457) at com.mysql.jdbc.ResultSetImpl.updateInt(ResultSetImpl.java:8475) at NewSet.Updatable.main(Updatable.java:42)
更新于： 30-Jul-2019
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