如何使用JDBC程序将null值设置/插入到行的某一列中？
您可以通过两种方式将空值插入SQL中的表：
将NULL值直接插入所需的列中，如下所示：
Insert into SampleTable values (NULL);
将''用作null
Insert into SampleTable values (NULL);
使用PreparedStatement对象将数据插入表中时，可以使用PreparedStatement接口的setNull()方法将空值设置为列。
pstmt.setNull(parameterIndex, sqlType);
示例
假设我们在数据库中有一个名为cricketers_data的表，其内容如下：
+------------+------------+---------------+----------------+-------------+ | First_Name | Last_Name | Date_Of_Birth | Place_Of_Birth | Country | +------------+------------+---------------+----------------+-------------+ | Shikhar | Dhawan | 1981-12-05 | Delhi | India | | Jonathan | Trott | 1981-04-22 | CapeTown | SouthAfrica | | Kumara | Sangakkara | 1977-10-27 | Matale | Srilanka | | Virat | Kohli | 1987-04-30 | Delhi | India | | Rohit | Sharma | 1987-04-30 | Nagpur | India | +------------+------------+---------------+----------------+-------------+
接下来的JDBC程序连接到数据库，并在其中插入一个新行，并将其出生位置的值设置为NULL。
import java.sql.Connection;
import java.sql.Date;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.Statement;
import java.sql.Types;
public class InsertingNull {
public static void main(String args[])throws Exception {
//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......");
//创建一个Statement对象
Statement stmt = con.createStatement();
//将值插入表
String query = "INSERT INTO cricketers_data VALUES (?, ?, ?, ?, ?)";
//创建一个PreparedStatement对象
PreparedStatement pstmt = con.prepareStatement(query);
pstmt.setString(1, "Ravindra");
pstmt.setString(2, "Jadeja");
pstmt.setDate(3, new Date(597396086000L));
//为列设置空值
pstmt.setNull(4, Types.NULL);
pstmt.setString(5, "India");
pstmt.execute();
System.out.println("Record inserted");
}
}输出结果
Connection established...... Record inserted......
如果检索cricketers_data表的内容，则可以观察到具有空值的新插入的记录。
mysql> select * from cricketers_data; +------------+------------+---------------+----------------+-------------+ | First_Name | Last_Name | Date_Of_Birth | Place_Of_Birth | Country | +------------+------------+---------------+----------------+-------------+ | Shikhar | Dhawan | 1981-12-05 | Delhi | India | | Jonathan | Trott | 1981-04-22 | CapeTown | SouthAfrica | | Lumara | Sangakkara | 1977-10-27 | Matale | Srilanka | | Virat | Kohli | 1987-04-30 | Delhi | India | | Rohit | Sharma | 1987-04-30 | Nagpur | India | | Ravindra | Jadeja | 1988-12-06 | NULL | India | +------------+------------+---------------+----------------+-------------+ 6 rows in set (0.00 sec)