在本教學將演示如何在JDBC應用程式中，從資料庫表中查詢資料記錄，在查詢語句中將使用asc和desc關鍵字按升序或降序對記錄進行排序。在執行以下範例之前，請確保您已經準備好以下操作：
username)和密碼(password)。使用JDBC應用程式查詢表中資料記錄需要以下步驟：
匯入包：需要包含包含資料庫程式設計所需的JDBC類的包。 大多數情況下，使用import java.sql.*就足夠了。
註冊JDBC驅動程式：需要初始化驅動程式，以便可以程式中開啟資料庫的通訊通道。
開啟連線：需要使用DriverManager.getConnection()方法來建立一個Connection物件，它表示與資料庫伺服器的物理連線。
執行查詢：需要使用型別為Statement的物件來構建和提交SQL語句來對表中的記錄進行排序。 這些查詢使用asc和desc子句對升序和降序進行資料排序。
清理環境：需要明確地關閉所有資料庫資源，而不依賴於JVM的垃圾收集。
複製以下範例程式碼儲存到檔案：SelectSortingData.java中，然後編譯並執行如下 -
//STEP 1. Import required packages
// See more detail at /20/213/8320.html
import java.sql.*;
public class SelectSortingData {
// JDBC driver name and database URL
static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
static final String DB_URL = "jdbc:mysql://localhost/jdbc_db";
// Database credentials
static final String USER = "root";
static final String PASS = "123456";
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();
// 按first欄位升序排序
System.out.println("Fetching records in ascending order by fist field...");
String sql = "SELECT id, first, last, age FROM student" +
" ORDER BY first ASC";
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);
}
// 按first欄位降序排序
System.out.println("Fetching records in descending order by fist field ...");
sql = "SELECT id, first, last, age FROM student" +
" ORDER BY first DESC";
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);
}
// 按ID欄位降序排序
System.out.println("Fetching records in descending order by ID field ...");
sql = "SELECT id, first, last, age FROM student" +
" ORDER BY id DESC";
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
編譯上面程式碼，如下 -
F:\worksp\jdbc> javac -Djava.ext.dirs=F:\worksp\jdbc\libs SelectSortingData.java
執行上面程式碼，如下 -
## 可先建立表或插入資料 -
## F:\worksp\jdbc> java -Djava.ext.dirs=F:\worksp\jdbc\libs InsertRecords
F:\worksp\jdbc>java -Djava.ext.dirs=F:\worksp\jdbc\libs SelectSortingData
Connecting to a selected database...
Fri Jun 02 00:42:39 CST 2017 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
Connected database successfully...
Creating statement...
Fetching records in ascending order by fist field...
ID: 100, Age: 18, First: C++, Last: Li
ID: 103, Age: 28, First: Java, Last: Ja
ID: 101, Age: 25, First: Python, Last: Py
ID: 102, Age: 30, First: Ruby, Last: Ru
Fetching records in descending order by fist field ...
ID: 102, Age: 30, First: Ruby, Last: Ru
ID: 101, Age: 25, First: Python, Last: Py
ID: 103, Age: 28, First: Java, Last: Ja
ID: 100, Age: 18, First: C++, Last: Li
Fetching records in descending order by ID field ...
ID: 103, Age: 28, First: Java, Last: Ja
ID: 102, Age: 30, First: Ruby, Last: Ru
ID: 101, Age: 25, First: Python, Last: Py
ID: 100, Age: 18, First: C++, Last: Li
Goodbye!
F:\worksp\jdbc>