preventing duplicate row insertion in php/mysql

Question

how do you prevent the entry of duplicate records in php mysql? validating input before insertion to the table.

i am currently building a user registration section f

Answer 1

i used the sql statement along with an if else statement.

mysql_select_db($database_speedycms, $speedycms);
$query_usercheck = "SELECT * FROM tbl_users WHERE username='$user' OR email='$email'";
$usercheck = mysql_query($query_usercheck, $speedycms) or die(mysql_error());
$row_usercheck = mysql_fetch_assoc($usercheck);
$totalRows_usercheck = mysql_num_rows($usercheck);

then

if ( $totalRows_usercheck > 0 )

display an error message to prevent any duplicates from being added

otherwise allow database insert