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Where Clause


This chapter provides an example on how to select records from a table using JDBC application. This would add additional conditions using WHERE clause while selecting records from the table. Before executing the following example, make sure you have the following in place:
  • To execute the following example you can replace the username and password with your actual user name and password.
  • Your MySQL or whatever database you are using, is up and running.
Required Steps

The following steps are required to create a new Database using JDBC application:
  • Import the packages: Requires that you include the packages containing the JDBC classes needed for the database programming. Most often, using import java.sql.* will suffice.
  • Register the JDBC driver: Requires that you initialize a driver so you can open a communications channel with the database.
  • Open a connection: Requires using the DriverManager.getConnection() method to create a Connection object, which represents a physical connection with a database server.
  • Execute a query: Requires using an object of type Statement for building and submitting an SQL statement to fetch records from a table, which meet the given condition. This Query makes use of the WHERE clause to select records.
  • Clean up the environment: Requires explicitly closing all database resources versus relying on the JVM's garbage collection.
Sample Code

Copy and paste the following example in JDBCExample.java, compile and run as follows:

//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 id >= 101 ";
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

Now, let us compile the above example as follows:

C:\>javac JDBCExample.java
C:\>

When you run JDBCExample, it produces the following result:

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: 102, Age: 30, First: Zaid, Last: Khan
ID: 103, Age: 28, First: Sumit, Last: Mittal
Goodbye!
C:\>
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