Thursday, April 18, 2013

perfect number check using php

A perfect number is a positive integer where the sum of all its positive divisors, except itself, is equal to the number itself. For example 6 is a perfect number as 1,2 and3 are its divisors and the sum of divisors=1+2+3=6. Here we have created a program that will take the number from the user and reports whether it is perfect or not

<?php
$num=6;
$perfectNo =0;
        for ($i = 1;$i < $num; $i++) {
            if ($num % $i == 0) {
                $perfectNo += $i;
               
            }
        }
        if ($perfectNo == $num) {
            echo("number is a perfect number");
        } else {
            echo("number is not a perfect number");
        }

Wednesday, April 17, 2013

MySQL LEFT, RIGHT JOIN tutorial

MySQL LEFT, RIGHT JOIN tutorial

MySQL joins are hard for beginners. At least for me when I was beginner.
I will try to explain the joins in the simplest possible way.
Join in MySQL is a query where you can join one or more tables.
For example we have two tables: products and buyers with the following structures.
Table products:
mysql> SELECT * FROM products;
+----+--------------+--------------+
| id | product_name | manufacturer |
+----+--------------+--------------+
|  1 | Shoes        | Company1     |
|  2 | Laptop       | Company2     |
|  3 | Monitor      | Company3     |
|  4 | DVD          | Company4     |
+----+--------------+--------------+
4 rows in set (0.00 sec)
Table buyers:
mysql> SELECT * FROM buyers;
+----+------+------------+----------+
| id | pid  | buyer_name | quantity |
+----+------+------------+----------+
|  1 |    1 | Steve      |        2 |
|  2 |    2 | John       |        1 |
|  3 |    3 | Larry      |        1 |
|  4 |    3 | Michael    |        5 |
|  5 | NULL | Steven     |     NULL |
+----+------+------------+----------+
5 rows in set (0.00 sec)

Left Join

mysql> SELECT buyer_name, quantity, product_name FROM buyers LEFT JOIN products ON
 buyers.pid=products.id;
+------------+----------+--------------+
| buyer_name | quantity | product_name |
+------------+----------+--------------+
| Steve      |        2 | Shoes        |
| John       |        1 | Laptop       |
| Larry      |        1 | Monitor      |
| Michael    |        5 | Monitor      |
| Steven     |     NULL | NULL         |
+------------+----------+--------------+
5 rows in set (0.00 sec)
What happened?
Mysql starts with the left table (buyers). For each row from the table buyers mysql scans the table products, finds the id of the product and returns the product name. Then the product name is joined with the matching row from the table buyers. For unmatched rows it returns null.
To make it simpler, the above query is same as (except the unmatched rows are not returned):
mysql> SELECT buyers.buyer_name, buyers.quantity, products.product_name FROM buyer
s,products WHERE buyers.pid=products.id;
+------------+----------+--------------+
| buyer_name | quantity | product_name |
+------------+----------+--------------+
| Steve      |        2 | Shoes        |
| John       |        1 | Laptop       |
| Larry      |        1 | Monitor      |
| Michael    |        5 | Monitor      |
+------------+----------+--------------+
4 rows in set (0.00 sec)

Right Join

mysql> SELECT buyer_name, quantity, product_name FROM buyers RIGHT JOIN products
 ON 
buyers.pid=products.id;
+------------+----------+--------------+
| buyer_name | quantity | product_name |
+------------+----------+--------------+
| Steve      |        2 | Shoes        |
| John       |        1 | Laptop       |
| Larry      |        1 | Monitor      |
| Michael    |        5 | Monitor      |
| NULL       |     NULL | DVD          |
+------------+----------+--------------+
5 rows in set (0.00 sec)
What happens here is Mysql starts with the Right table (products). For each id from the table products MySQL scans the left table - buyers to find the matching pid. When it finds the matching pid it returns the buyer_name and the quantity. For unmatched rows it returns null. From my example above it returns NULL for DVD because no one bought DVD.