Ubuntu Service not connected to MySQL, how to solve

Ubuntu service not even on MySQL
With Ubuntu service 12.04 version, Apache install no problem, Web page can be accessed, MySQL server can be accessed by command. But using the following database connection code is not possible. What's going on here.
Did not jump out of the error prompt
$con = mysql_connect ("localhost", "root", "123");
if (! $con)
{
Die (' Could not connect: '. Mysql_error ());
}

$db _selected = mysql_select_db (' buy ', $con);

if (! $db _selected)
{
Die ("can\-t use test_db:". Mysql_error ());
}
------Solution--------------------
$con = mysql_connect ("127.0.0.1", "root", "123"); Can I link it? It is most likely a permissions issue.
How do you link MySQL to Ubuntu?
$ mysql-h localhost-u root-p;?
"Show grants" to see what to return?
What does "Select User, host from Mysql.user" return?
------Solution--------------------
What do you mean, no? What is the error message?

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