why php tag is not working if i store and show it in wp_head?

Question

hi i used wp_head a couple of times.I echoed some values it works like below

function test()
{
echo "hello am visible";
}
add_action('wp_head','test');

but if i store a php code in db and retrieve it to a variable and echoed it is not working, here is the sample

<?php echo "i will go to db and come again"; ?>

i stored the above value in LONGTEXT format in db as trial then i selected the table and assigned it to a variable like below

$output = $result->trial;

Here come the problem part

function test()
    {
    //after retrieve 
    echo $output;
    }
add_action('wp_head','test');

this way it is not working.i can't able to see i will go to db and come again. What is the problem? Thanks