Can i use multiple databases in one applicationin php? - php

Question

I am Developing the simple application,the application related to database operations.
My doubt is how can i connect to multiple databases same time.
how can php knows which databases the data will store.
If the user enter the data which database it will enter,both databases or one database.
Please answer my question.i have struggling a lot for this question.

Answer 1

If you use PHP5 (And you should, given that PHP4 has been deprecated), you should use PDO, since this is slowly becoming the new standard. One (very) important benefit of PDO, is that it supports bound parameters, which makes for much more secure code.
You would connect through PDO, like this:
try {
$db = new PDO('mysql:dbname=databasename;host=127.0.0.1', 'username', 'password');
} catch (PDOException $ex) {
echo 'Connection failed: ' . $ex->getMessage();
}
(Of course replace databasename, username and password above)
You can then query the database like this:
$result = $db->query("select * from tablename");
foreach ($result as $row) {
echo $row['foo'] . "\n";
}
Or, if you have variables:
$stmt = $db->prepare("select * from tablename where id = :id");
$stmt->execute(array(':id' => 42));
$row = $stmt->fetch();
If you need multiple connections open at once, you can simply create multiple instances of PDO:
try {
$db1 = new PDO('mysql:dbname=databas1;host=127.0.0.1', 'username', 'password');
$db2 = new PDO('mysql:dbname=databas2;host=127.0.0.1', 'username', 'password');
} catch (PDOException $ex) {
echo 'Connection failed: ' . $ex->getMessage();
}

Answer 2

Yes you can.. by using two connection strings..
$mysqli1 = new mysqli('HOST1', 'USER1', 'PASSWORD1', 'DB_NAME1');
$mysqli2 = new mysqli('HOST2', 'USER2', 'PASSWORD2', 'DB_NAME2');
and your queries should be like
$result1 = $mysqli1->query('query ......');
and
$result2 = $mysqli2->query('query ......');

Answer 3

Of course you can given example below add more connections if you want:
Class database
{
private oracleDatabase;
private mysqlDatabase;
public function connOracle() {
$db = "";
$user = "";
$password = "";
try {
$this->oracleDatabase = new PDO("oci:dbname=".$db,$user,$password);
} catch(PDOException $e){
echo "Can't connect to database (Oracle). ". $e->getMessage();
}
}
public function connMysql() {
$db = "";
$user = "";
$password = "";
try {
$this->mysqlDatabase = new PDO("mysql:dbname=".$db,$user,$password);
} catch(PDOException $e){
echo "Can't connect to database (Mysql). ". $e->getMessage();
}
}
}

Answer 4

Be carefull if you are using two databases on the same server at the same time. By default mysql_connect returns the same connection ID for multiple calls with the same server parameters, which means if you do
<?php
$db1 = mysql_connect(...stuff...);
$db2 = mysql_connect(...stuff...);
mysql_select_db('db1', $db1);
mysql_select_db('db2', $db2);
?>
then $db1 will actually have selected the database 'db2', because the second call to mysql_connect just returned the already opened connection ID !
You have two options here, eiher you have to call mysql_select_db before each query you do, or if you're using php4.2+ there is a parameter to mysql_connect to force the creation of a new link.
Use this below link to refer.What you have asked here.
PHP Documentation

Answer 5

Yes, you may use multiple database in one application, but the main thing is when you are communicating with the dbname, you have to specify that dbname also so than script will communicate with only that db in which you had defined. Ex.
$db1 = mysql_connect(...stuff...);
$db2 = mysql_connect(...stuff...);
mysql_select_db('db1', $db1);
mysql_select_db('db2', $db2);
$resultsa = mysql_query('SELECT * FROM table_a', $dbname) or die('Could not query database_a');

Answer 6

Yes you can connect multiple databases.
open your php.ini file and give me your database details like
port number,username,password.
And after that you can give the queries like this in your applications
$db1 = mysql_connect($hostname, $username, $password);
$db2 = mysql_connect($hostname, $username, $password, true);
mysql_select_db('database1', $db1);
mysql_select_db('database2', $db2);
Then to query database 1, do this:
mysql_query('select * from tablename', $dbh1);
and for database 2:
mysql_query('select * from tablename', $dbh2);
i think this is work fine for your question.

Answer 7

Yes you can, in very basic terms, you do it like this:
http://au1.php.net/function.mysql-connect
$conn = mysql_open($host, $username, $password, true);
To connect to multiple databases on the same server:
$dblink1 = mysql_select_db('database_a', $conn);
$dblink2 = mysql_select_db('database_b', $conn);
To get results from two databases:
$resultsa = mysql_query('SELECT * FROM table_a', $dblink1) or die('Could not query database_a');
$resultsb = mysql_query('SELECT * FROM table_b', $dblink2) or die('Could not query database_b');
edit - keep in mind that the mysql_ functions aren't available in recent PHP releases because they've been removed.
Warning
This extension is deprecated as of PHP 5.5.0, and will be removed in
the future. Instead, the MySQLi or PDO_MySQL extension should be used.
See also MySQL: choosing an API guide and related FAQ for more
information.