In mysql database i have this column called:
Name: Date
Type: datetime
I have few values in that column:
2009-01-05 01:23:35
2009-03-
You don't need to use PHP, MySQL has a function to get the current date:
SELECT field FROM table WHERE DATE(column) = CURDATE()
Documentation: CURDATE, DATE.
If your column is only ever going to need the date part and never the time, you should change your column type to DATE. If you insist on doing it through PHP, it is the same thing, really:
$today = date('Y-m-d');
$query = mysql_query("
SELECT field FROM table WHERE DATE(column) = '$today'
");