input SQL data through text box and get nothing?

I want to add SQL command through a textbox in the form using post
method,but when i execute the following file, nothing is added to the
database.
I can add
$sqlol = "update acc_account
set user_name='k'
where accountid=1";
to the database if it was added to the file but when i use $result =
mysql_query($sql); which execute the query, it get nothing. However,
the $sql statement do print out on the screen using print.

Any idea?

<?php
$conn=mysql_connect('localhost', 'shytr8');

if(!$conn)
{print "Error- Could not connect to MYSQL";
exit;}

$er=mysql_select_db("test");

if(!$er){
print "Error- Could not create er";
$query = "CREATE DATABASE test";
mysql_query($query);}



$sql=$_POST[SQLcommand];
$result = mysql_query($sql);
?>

.

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