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， 在查詢選擇記錄時使用Like子句新增其他條件。 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，以從滿足給定條件的表中獲取記錄。 此查詢使用LIKE子句來選擇所有first欄位的值包含「y」字母的學生資訊。
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：SelectLikeClause.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 SelectLikeClause {
// 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();
// Extract records without any condition.
System.out.println("Fetching records without condition...");
String sql = "SELECT id, first, last, age FROM student";
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 student" +
" WHERE first LIKE '%y%' ";
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 SelectLikeClause.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 SelectLikeClause
Connecting to a selected database...
Fri Jun 02 00:33:58 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 without condition...
ID: 100, Age: 18, First: C++, Last: Li
ID: 101, Age: 25, First: Python, Last: Py
ID: 102, Age: 30, First: Ruby, Last: Ru
ID: 103, Age: 28, First: Java, Last: Ja
Fetching records with condition...
ID: 101, Age: 25, First: Python, Last: Py
ID: 102, Age: 30, First: Ruby, Last: Ru
Goodbye!
F:\worksp\jdbc>
在執行上面語句後，可以看到只有 first 欄位的值中包含有y字母的兩條(ID為101和102)記錄查詢顯示出來。