MySQL: LIKE and First character

LIKE supports wildcards. % means any number of characters (including zero), and _ means any one character`

stationname LIKE 'cheese%'

This would match cheese and cheese2.

You can use the % for the first issue too.

stationname LIKE 'a%'

This will find all words that start with 'a'.

I'm trying to select all the rows where stationname starts with $_GET['letter']

MySQL has a LEFT function which seems to be what you're looking for. So basically we extract the first letter of the stationname and compare it agains your letter:

 where left(stationname, 1) = '" . mysql_real_escape_string($_GET['letter']) . "'";

Is there any way to select both cheese and cheese2?

Well here the solution is a little smelly, as you should check whether cheese is contained in cheese2 and also whether cheese2 is contained in cheese. Try this:

where stationname like '%" . mysql_real_escape_string($_POST['search']) .
  "%' OR '" . mysql_real_escape_string($_POST['search']) .
  "' like concat('%', stationname, '%')";

for second.

 $query = "   SELECT
                        stationname
                    FROM
                        stations
                    WHERE
                        stationname 
                    LIKE
                        '". mysql_real_escape_string($_POST['search']) ."%'
        ";