Comments - Access to more databases

This sounds like a connection definition problem. You should be using two different connections, one per database. When building your queries, you should be referencing the database connection for the database you want to query.

Example:

$cnn_db1 = mysqli_connect($Servername, $Username, $Password, $Database1);
$cnn_db2 = mysqli_connect($Servername, $Username, $Password, $Database2);
$rst_query1 = mysqli_query($cnn_db1, "SELECT * FROM Users")
$rst_query2 = mysqli_query($cnn_db2, "SELECT * FROM Users")
mysqli_free_result($rst_query1);
mysqli_free_result($rst_query2);
mysqli_close($cnn_db2);
mysqli_close($cnn_db1);

If you don't specify a database in the identifier name, the default, or current, database, will be used. See USE. To avoid ambiguity, you can use the dbname.tablename syntax. See Identifier Qualifiers and SELECT.

Thank you Ian. I'll see USE option because I would like to avoid having to enter all the prefixes with the database name !