How to Connect to Multiple MySQL Databases from a Single PHP Web Page?

How to Connect to Multiple MySQL Databases on a Single Web Page Using PHP

To access information from multiple MySQL databases on a PHP webpage, you can utilize multiple connections. Previously, the mysql_connect() function was used for database connection, but it's now deprecated.

Method 1: Using Multiple MySQL Connections

You can create multiple MySQL connections using the mysql_connect() function with the $new_link parameter set to true to open a new connection for each database. For example:

$dbh1 = mysql_connect($hostname, $username, $password);
$dbh2 = mysql_connect($hostname, $username, $password, true);

mysql_select_db('database1', $dbh1);
mysql_select_db('database2', $dbh2);

To query each database, pass the appropriate connection identifier along with the query. For example:

mysql_query('select * from tablename', $dbh1); // Query database1
mysql_query('select * from tablename', $dbh2); // Query database2

Alternatively, if you don't specify a connection identifier, the last opened connection will be used.

Method 2: Using PDO (Preferred Method)

Instead of using the deprecated mysql functions, it's recommended to use PDO (PHP Data Objects) for database connectivity. With PDO, you can establish multiple connections using different options:

a. Separate Connections:

$db1 = new PDO('mysql:host=localhost;dbname=database1', 'username', 'password');
$db2 = new PDO('mysql:host=localhost;dbname=database2', 'username', 'password');

b. Shared Connection:

If the user has access to both databases through the same connection, you can specify the database in the query:

$db = new PDO('mysql:host=localhost;', 'username', 'password');
$db->query('SELECT * FROM database1.table_name'); // Query database1
$db->query('SELECT * FROM database2.table_name'); // Query database2

These approaches allow you to access and manage data from multiple MySQL databases within the same PHP webpage.

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