How to use multiple MYSQL databases in a project

If your databases are located on same MySQL server.You don’t need two connections, you can access them both as unique user.

You also don’t need to select a DB. Just use the database-name as prefix when specifying the tables. That’s it.

[php]
<?php

mysql_connect("localhost","username","password") or die(mysql_error());

$query = "SELECT * FROM database1.tablename";

$result = mysql_query($query)or die(mysql_error());

var_dump($result);

$query2 = "SELECT * FROM database2.tablename";

$result2 = mysql_query($query2)or die(mysql_error());

var_dump($result2);

?>
[/php]

Or if you want to select database, you can do

Please note there can only be one active DB at a time, it will work in this way:

[php]
<?php

$conn1 = mysql_connect("localhost","username","password") or die(mysql_error());

$conn2 = mysql_connect("localhost","username","password",true) or die(mysql_error());

mysql_select_db("database1",$conn1);

// tablename is a table of database1

$query = "SELECT * FROM tablename";

$result = mysql_query($query,$conn1);

var_dump($result);

mysql_select_db("database2",$conn2);

// tablename is a table of database2

$query2 = "SELECT * FROM tablename";

$result2 = mysql_query($query2,$conn2);

var_dump($result2);

?>
[/php]

Although there’s no need for 2 connections; you can select both DB’s using the same connection.

You can make multiple calls to mysql_connect(), but if the parameters are the same you need to pass true for the ‘$new_link’ (fourth) parameter, otherwise the same connection is reused.

So then you have to do is

[php]
<?php

$db_conn1 = mysql_connect($hostname, $username, $password);

$db_conn2 = mysql_connect($hostname, $username, $password, true);

mysql_select_db(‘database1’, $db_conn1);

mysql_select_db(‘database2’, $db_conn2);

//Then to query database 1, do

mysql_query(‘select * from tablename’, $db_conn1);

//and for database 2

mysql_query(‘select * from tablename’, $db_conn2);

?>
[/php]

It is used if MySQL server of database is different.