How to Select a MySQL Database
If you don’t select the MySQL database in the connect function, you can select the database by using the mysqli_select_db function. You can also use this function to select a different database at any time in your script. The format is
mysqli_select_db($cxn,"databasename") or die ("message");
If you’re using the mysql functions, rather than the mysqli functions, you must select the database in a separate function, using mysql_select_db.
Fill in the following information:
*cxn: The variable that contains the connection information.
databasename: The name of the database.
*message: The message that’s sent to the browser if the database can’t be selected. The selection might fail because the database can’t be found, which is usually the result of a typo in the database name.
For instance, you can select the database Customer with the following statement:
mysqli_select_db($cxn,"Customer") or die ("Couldn't select database.");
If mysqli_select_db can’t select the database, the script stops running and the message Couldn't select database. is sent to the browser.
The database stays selected until you select a different database. To select a different database, just use a new mysqli_select_db function statement.