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Monday, May 12, 2008

Storing and Retrieving Data from MySQL Database

Storing and Retrieving Data from MySQL Database

You may first want to read Installing, Configuring and Testing MySQL Database Server on 'localhost', About MySQL, Databases and SQL Commands.

Now that you have installed MySQL database server and have learnt some SQL commands to query MySQL, its time to use our knowledge to do what database servers are used for, storing and retrieving data.

To make for a nice example, we’ll create a simple Phonebook Application which would store phone numbers and names of peoples. It’d be able to illustrate the storage and retrieval of data from database quite well.

OK let’s first start with the datable design. We’d need to create a database first and table in that database. One table is enough because we only need to store name and phone number which should be stored in the same table. For the table we should have two fields (column), one for name and the other for phone number. Both can be of data type (MySQL) VARCHAR as we don’t need to even the phone number to be interpreted as a number. The creation of the database and table can be done with the following SQL query:

CREATE DATABASE one;
CREATE TABLE phbook (name VARCHAR(20), phno VARCHAR(20));

For inserting data to the table just created we’ll use the following SQL query:

INSERT INTO phbook(name, phno) VALUES (‘$name’,’$phno’);

And retrieval of data can be done using:

SELECT * FROM phbook;

[Please read About MySQL, Databases and SQL Commands of you don’t understand these.]

One thing different with the above SQL query is that unlike all the other queries above, it ‘return’ data, when queried like :

$result=$db->query("select * from phno");

‘$result’ variable will contain the data retrieved from MySQL as per the query. In this case, all (*) the rows and columns i.e. the whole table.

The number of rows returned can be known by the 'num_rows' member function as follows::

$num_rows=$result->num_rows;

And each row of data can be retrieved one-by-one from the ‘$result’ object by the following function:

$row=$result->fetch_row();

[NOTE: After querying the database for data retrieval, we work with the data object returned ($result) and not with the database ($db) to work with the data.]

Now since ‘$row’ contains one row having two columns (fields), name and phno, each of it can be separately accessed using the indices:

$name=$row[0];
$phno=$row[1];

yeah, ‘fetch_row()’ function returns an array containing different data fields as different elements.

Now we have enough knowledge to clearly understand the code, here it is:

<?php
//----My Phone Book----
//Copyright 2008 http://learning-computer-programming.blogspot.com/
//This code is free to use and republish but credit 
//and copyright information must remain intact.
//-------------------------------

//connect to MySQL
//provide your 'username' and 'pass'
//change 'localhost' to the MySQL server
//host, if not using on 'local server'
$db=new mysqli('localhost','-USERNAME-','-PASS-');
//if 'save' button was pressed
//uesr wants to store phone number
if(isset($_POST['save']))
{
    
$name=trim($_POST['name']);
    
$phno=trim($_POST['phno']);
    
    
//if data supplied are not empty
    
if(!$name=='' || !$phno=='')
    {
        
//if this is the first time
        //and database is not craeted
        
if(!$db->select_db('one'))
            
//create the database
            
$db->query('create database one');
        
        
//select the databasw to work with
        
$db->select_db('one');
            
        
//if table is not craeted, craete it
        
if(!$db->query('select * from phno'))
            
$db->query('create table phno(name varchar(50), phnum varchar(20))');
        
        
//ready to insert data
        
$db->query("insert into phno (name, phnum) values ('$name', '$phno')");
    }
}
//show the form
?>
<html>
<head>
<title>My Phone Book</title>
</head>

<body>
<h1>My Phone Book</h1>
<h2 style="background: #000; color: #fff;">Store New Phone Number</h2>
<form name="form1" id="form1" method="post" action="">
  <table width="250" border="0" cellspacing="0" cellpadding="0">
    <tr> 
      <td width="83">Name</td>
      <td width="417"><input name="name" type="text" id="name" /></td>
    </tr>
    <tr> 
      <td>Ph. No.</td>
      <td><input name="phno" type="text" id="phno" value=""></td>
    </tr>
    <tr> 
      <td><input name="save" type="submit" id="save" value="Save" /></td>
      <td><input type="reset" name="Submit2" value="Reset" /></td>
    </tr>
  </table>
</form>
<h2 style="background: #000; color: #fff;">Previously Stored</h2>
</body>
</html>
<?php
//----DISPALY PREVIOUSLY STORED PH. NUMBERS----

//if database does not exits
//first time operation
if(!$db->select_db('one'))
{
    echo 
"<p><i>NONE</i></p>";
    exit;
}
//else
$result=$db->query("select * from phno");
//find number of rows
$num_rows=$result->num_rows;
//process all the rows one-by-one
for($i=0;$i<$num_rows;$i++)
{
    
//fetch one row
    
$row=$result->fetch_row();
    
//print the values
    
echo "<p><span style=\"font-size: 200%;\">$row[0]: </span> $row[1]</p>";
}
//close MySQL connection
$db->close();
?>

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