Natural Left Join
In this program we are going to join the two table by
using the servlets and the result will be displayed in the browser. This join
will be natural left join.
To join the tables firstly it is important to make a
connection between the java class and the database. In our program we are using
the MySql database. To join the table in a natural left join manner it is important to have those
tables in our database. First of all make a class named ServletNaturalJoiningTables.
The name of the class should be such that it becomes clear that what the program
is going to do. The logic of the program will be written inside the doGet()
method which takes two arguments HttpServletRequest and HttpServletResponse.
call the method getWriter() of the PrintWriter class, which is
responsible for writing the contents on the browser. Our priority is to join the
two tables so pass a query in prepareStatement() method which will return
the PreparedStatement object.
The result will be displayed to you by the object of
the PrintWriter class.
The code of the program is given below:
import java.sql.*;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class ServletNaturalJoiningTables extends HttpServlet{
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException{
response.setContentType("text/html");
PrintWriter pw = response.getWriter();
String connectionURL = "jdbc:mysql://localhost/zulfiqar";
Connection connection;
try{
Class.forName("org.gjt.mm.mysql.Driver");
connection = DriverManager.getConnection
(connectionURL, "root", "admin");
PreparedStatement pst =
connection.prepareStatement("SELECT * FROM "+"emp_details"+"
NATURAL LEFT JOIN "+"emp_sal");
ResultSet rs = pst.executeQuery();
pw.println("UserId" + "\t" + "Firstname" +
"\t" + "Salary"+"<br>");
while(rs.next()){
String id = rs.getString("userId");
String name = rs.getString("Name");
String sal = rs.getString("salary");
pw.println(id + "\t\t" + name + "\t\t" + sal + "<br>");
}
}
catch (Exception e) {
pw.println("The statement is not executed");
}
}
}
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web.xml file for this program:
<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE web-app
PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd">
<web-app>
<servlet>
<servlet-name>Zulfiqar</servlet-name>
<servlet-class>ServletNaturalJoiningTables</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Zulfiqar</servlet-name>
<url-pattern>/ServletNaturalJoiningTables</url-pattern>
</servlet-mapping>
</web-app>
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The output of the program is given below:
Download this
example:
