Monday, May 24, 2010

Cross Join Tables in a Specific Database

This section introduces you to the cross join between two tables. The cross join operation retrieves data between two tables as a Cartesian product of set theory in mathematics. Each row will get multiplied by other rows. If one table has three rows and the second row has two rows, then the cartesian of two table will be six. See brief description below:

Cross Join: This is a type of join table operation. It is a same as inner and outer join operation. The cross join is used to retrieve data from tables as Cartesian product format of set theory in mathematics. All rows are shown to be multiply by to another tables' rows.

Description of program:

First of all this program establishes the connection, after that the cross join operation will be performed between two tables. Both tables hold some specific fields and it's values. While you retrieve data in cross join format, it shows that the each row will get multiply by other rows.

Description of code:

SELECT *FROM employee, Emp_sal :
This code is used to retrieve data form both tables as Cartesian product format (multiply the field to each other).

Here is the code of program:

import java.sql.*;

public class CrossJoinTable{
public static void main(String[] args) {
System.out.println("Natural Left Join Tables Example!");
Connection con = null;
con = DriverManager.getConnection
Statement st = con.createStatement();
ResultSet res = st.executeQuery
("SELECT *FROM "+"employee"+","+"Emp_sal"); //Cross Join two tables
System.out.println("Emp_name" + "\t" + "Emp_ed" + "\t" + "Emp_sal");
String name = res.getString("Emp_name");
int ed = res.getInt("Emp_ed");
int sal = res.getInt("Emp_sal");
System.out.println(name + "\t\t" + ed + "\t" + sal);
catch (SQLException s){
System.out.println("SQL statement is not executed!");
catch (Exception e){
Download this example.

Table:- employee:

Emp_ed Emp_name




Table:- Emp_sal:

Emp_name Emp_sal


Output of program:


C:\vinod\jdbc\jdbc\jdbc-mysql>java CrossJoinTable
Natural Left Join Tables Example!
Emp_name Emp_ed Emp_sal
santosh 2 8000
santosh 2 4500
deepak 10 8000
deepak 10 4500
Aman 13 8000
Aman 13 4500

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