How Can I Access Multiple MySQL Databases from a Single PHP Webpage?

Accessing Multiple MySQL Databases on a Single Webpage with PHP

Connecting to multiple MySQL databases from a single PHP webpage is possible using the mysql_connect function. However, certain considerations should be made to ensure correct database usage.

Connecting Multiple Databases

To connect to multiple databases, make multiple calls to mysql_connect with the same parameters. Pass true as the fourth (new link) parameter to establish a new connection for each database. For example:

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

Selecting Databases

Once connected, use mysql_select_db to specify which database to query from. Pass the link identifier as the second parameter. For example:

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

Querying Databases

To query a specific database, pass the corresponding link identifier as the first parameter to mysql_query. If no link identifier is specified, the last connection created will be used. For example:

// Query database 1
mysql_query('select * from tablename', $dbh1);

// Query database 2
mysql_query('select * from tablename', $dbh2);

Alternative Options

If the user has access to both databases on the same host, consider these alternatives:

• Single Connection with mysql_select_db(): Keep one connection open and switch databases using mysql_select_db(). However, this approach can lead to inconsistencies.
• Database Specification in Queries: Specify the database name in your queries (e.g., SELECT * FROM database2.tablename). This option can be cumbersome, especially for complex queries.

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