如何使用JDBC API将自动增量设置为表中的现有列？
您可以使用ALTERTABLE命令向表中的列添加/设置自动增量约束。
语法
ALTER TABLE table_name ADD id INT PRIMARY KEY AUTO_INCREMENT
假设我们在数据库中有一个名为Dispatches的表，其中有7列，分别是id，CustomerName，DispatchDate，DeliveryTime，Price和Location，其描述如下所示：
+--------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------------+--------------+------+-----+---------+-------+ | ProductName | varchar(255) | YES | UNI | NULL | | | CustomerName | varchar(255) | YES | | NULL | | | DispatchDate | date | YES | | NULL | | | DeliveryTime | time | YES | | NULL | | | Price | int(11) | YES | | NULL | | | Location | text | YES | | NULL | | | ID | int(11) | NO | PRI | NULL | | +--------------+--------------+------+-----+---------+-------+
下面的JDBC程序与MySQL数据库建立连接，添加一个名为Id的列，并将值设置为id列作为自动增量。
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
public class SettingAutoIncrement {
public static void main(String args[]) throws SQLException {
//注册驱动程序
DriverManager.registerDriver(new com.mysql.jdbc.Driver());
//获得连接
String mysqlUrl = "jdbc:mysql://localhost/mydatabase";
Connection con = DriverManager.getConnection(mysqlUrl, "root", "password");
System.out.println("Connection established......");
//创建语句
Statement stmt = con.createStatement();
//设置列ID自动递增
String query = "ALTER TABLE Sales ADD id INT PRIMARY KEY AUTO_INCREMENT";
stmt.execute(query);
stmt.executeBatch();
System.out.println("Table altered......");
}
}输出结果
Connection established...... Table altered......
如果使用“选择”命令检索“销售”表的内容，则可以看到名为id的列已使用自动递增的整数值添加到表中。
mysql> select * from Sales; +-------------+--------------+--------------+--------------+-------+----------------+----+ | ProductName | CustomerName | DispatchDate | DeliveryTime | Price | Location | id | +-------------+--------------+--------------+--------------+-------+----------------+----+ | Key-Board | Raja | 2019-09-01 | 08:51:36 | 7000 | Hyderabad | 1 | | Earphones | Roja | 2019-05-01 | 05:54:28 | 2000 | Vishakhapatnam | 2 | | Mouse | Puja | 2019-03-01 | 04:26:38 | 3000 | Vijayawada | 3 | | Mobile | Vanaja | 2019-03-01 | 04:26:35 | 9000 | Vijayawada | 4 | | Headset | Jalaja | 2019-03-01 | 05:19:16 | 6000 | Vijayawada | 5 | +-------------+--------------+--------------+--------------+-------+----------------+----+ 5 rows in set (0.00 sec)