Hello, i'm very new here in these forums.
I'm making a webpage for registration for my online game's server.
My problem is in the registering part, i've got the query to register the new user on the database, but first i need to check if the name of the account in the field isn't used yet. My code to do so is:

$query = mssql_query("SELECT * FROM memb_info WHERE memb___id = ".$_POST['cuenta']."");
 // memb_info is the table, memb___id is the accountname

if ($query) {print "does exist"; }
// just was a test

the problem is, if i type an existing account name, look which is the error:

Warning: mssql_query() [function.mssql-query]: message: The name of the column 'armakapo' is not valid. (severity 16) in C:\xampp\htdocs\caca.php on line 15

I guess it's searching for COLUMNS in the memb_info table, instead of ROWS.
because if i put in the account field "memb___id" (a name of a column), it says "does exist"
so, can you help me to make it search for a row instead of a column name? thanks you very much!