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Creating Database-Independent Applications With PEAR DB
Switch from one database to another without having to re-code your application

| Sweet Symbolism |

Before getting started with the code, you'll need to initialize the SQL table I'll be using throughout this tutorial. Pop open your MySQL command-line client, and enter the following SQL commands:

CREATE TABLE `symbols` (
  `id` int(11) NOT NULL auto_increment,
  `country` varchar(255) NOT NULL default '',
  `animal` varchar(255) NOT NULL default '',
  PRIMARY KEY  (`id`)
INSERT INTO `symbols` VALUES (1, 'America', 'eagle');
INSERT INTO `symbols` VALUES (2, 'China', 'dragon');
INSERT INTO `symbols` VALUES (3, 'England', 'lion');
INSERT INTO `symbols` VALUES (4, 'India', 'tiger');
INSERT INTO `symbols` VALUES (5, 'Australia', 'kangaroo');

You can enter these commands either interactively or non-interactively through the MySQL client program. Read http://dev.mysql.com/doc/mysql/en/mysql.html for more information on how to use the MySQL client, and the tutorial at http://www.melonfire.com/community/columns/trog/article.php?id=39 to understand what each of the SQL commands above does. SQL is a lot like spoken English, so it won't take you very long to pick it up.

Once the data has been imported, run a quick SELECT query to check if everything is working as it should:

mysql> SELECT * FROM symbols;
| id | country  | animal  |
|  1 | America  | eagle    |
|  2 | China    | dragon  |
|  3 | England  | lion    |
|  4 | India    | tiger    |
|  5 | Australia | kangaroo |
5 rows in set (0.06 sec)

You can do the same thing with PHP, as follows:

<head><basefont face="Arial"></head>

// open connection
$connection = mysql_connect("localhost", "john", "doe") or die ("Unable to connect!");

// select database
mysql_select_db("db2") or die ("Unable to select database!");

// create and execute query
$query = "SELECT country, animal FROM symbols";
$result = mysql_query($query) or die ("Error in query: $query. " . mysql_error());

// check for returned rows
if (mysql_num_rows($result) > 0) {
    // print them
    echo "<table cellpadding=10 border=1>";
    while($row = mysql_fetch_row($result)) {
          echo "<tr>";
          echo "<td>" . $row[0] . "</td>";
          echo "<td>" . $row[1] . "</td>";
          echo "</tr>";
    echo "</table>";
} else {
    // or print status message
    echo "No rows found!";

// free result set memory

// close connection


Most of this should already be familiar to you. The script above connects to the database, executes a query, retrieves the result and iterates through it. Fairly simple, except for one glaring flaw: because it uses MySQL-specific functions throughout, it's going to crash and burn the second you switch the data over to a PostgreSQL or Oracle RDBMS. Which is where the database abstraction layer comes in.

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