JDBC LIKE子句实例
本在线教程介绍了如何使用JDBC应用程序表中选择记录的一个例子。这里使用LIKE子句,而从表中选择记录添加附加条件。执行下面的示例之前,请确保如下:
-
执行下面的例子中,请使用实际的用户名和密码代替username和password。
-
MySQL或者其他数据库,正在使用:启动和运行。
所需步骤:
使用JDBC应用程序创建一个新的数据库需要执行以下步骤:
-
导入包:要求包括含有需要进行数据库编程的JDBC类的包。大多数情况下,使用 import java.sql.* 。
-
注册JDBC驱动程序:要求初始化驱动程序,使它可以与数据库打开一个通信通道。
-
打开一个连接:要求使用DriverManager.getConnection()方法创建一个Connection对象,它代表与数据库服务器的物理连接。
-
执行一个查询:需要使用类型Statement对象建立并提交一个SQL语句从符合给定条件的表获取记录。这使得查询使用LIKE子句来选择记录选择所有名字以 "za" 开始的学生。
-
清理环境:需要明确地关闭所有的数据库资源相对于依靠JVM的垃圾收集。
示例代码:
复制过去的下面的例子中JDBCExample.java,编译并运行,如下所示:
//STEP 1. Import required packages import java.sql.*; public class JDBCExample { // JDBC driver name and database URL static final String JDBC_DRIVER = "com.mysql.jdbc.Driver"; static final String DB_URL = "jdbc:mysql://localhost/STUDENTS"; // Database credentials static final String USER = "username"; static final String PASS = "password"; public static void main(String[] args) { Connection conn = null; Statement stmt = null; try{ //STEP 2: Register JDBC driver Class.forName("com.mysql.jdbc.Driver"); //STEP 3: Open a connection System.out.println("Connecting to a selected database..."); conn = DriverManager.getConnection(DB_URL, USER, PASS); System.out.println("Connected database successfully..."); //STEP 4: Execute a query System.out.println("Creating statement..."); stmt = conn.createStatement(); // Extract records without any condition. System.out.println("Fetching records without condition..."); String sql = "SELECT id, first, last, age FROM Registration"; ResultSet rs = stmt.executeQuery(sql); while(rs.next()){ //Retrieve by column name int id = rs.getInt("id"); int age = rs.getInt("age"); String first = rs.getString("first"); String last = rs.getString("last"); //Display values System.out.print("ID: " + id); System.out.print(", Age: " + age); System.out.print(", First: " + first); System.out.println(", Last: " + last); } // Select all records having ID equal or greater than 101 System.out.println("Fetching records with condition..."); sql = "SELECT id, first, last, age FROM Registration" + " WHERE first LIKE '%za%' "; rs = stmt.executeQuery(sql); while(rs.next()){ //Retrieve by column name int id = rs.getInt("id"); int age = rs.getInt("age"); String first = rs.getString("first"); String last = rs.getString("last"); //Display values System.out.print("ID: " + id); System.out.print(", Age: " + age); System.out.print(", First: " + first); System.out.println(", Last: " + last); } rs.close(); }catch(SQLException se){ //Handle errors for JDBC se.printStackTrace(); }catch(Exception e){ //Handle errors for Class.forName e.printStackTrace(); }finally{ //finally block used to close resources try{ if(stmt!=null) conn.close(); }catch(SQLException se){ }// do nothing try{ if(conn!=null) conn.close(); }catch(SQLException se){ se.printStackTrace(); }//end finally try }//end try System.out.println("Goodbye!"); }//end main }//end JDBCExample
现在来编译上面的例子如下:
C:>javac JDBCExample.java C:>
当运行JDBCExample,它会产生以下结果:
C:>java JDBCExample Connecting to a selected database... Connected database successfully... Creating statement... Fetching records without condition... ID: 100, Age: 30, First: Zara, Last: Ali ID: 102, Age: 30, First: Zaid, Last: Khan ID: 103, Age: 28, First: Sumit, Last: Mittal Fetching records with condition... ID: 100, Age: 30, First: Zara, Last: Ali ID: 102, Age: 30, First: Zaid, Last: Khan Goodbye! C:>