need help with an IF statement

I have this code:


if (isset($_GET['un']) AND isset($_GET['ln'])){

$un = $_GET['un'];
$ln = $_GET['ln'];

$query = mysql_query("INSERT INTO users ( username, link ) VALUES ('$un',
'$ln')");

if(!$query) die("Invalid query: " . mysql_error());

$result = mysql_query("SELECT link FROM links WHERE ID=$ln") or
die("Invalid query: " . mysql_error());

$y = mysql_fetch_array($result);

$go_link = $y['link'];

header("Location: $go_link");

exit();

}else{
echo "The required criteria was not found in the link.";

}




I need to write an IF statement that will only add $un and $ln to the table
users if the last one added was not the same username as this one (if it's
the same link, that's ok). For the ELSE part, it should still forward them
on to $go_link. Can anyone help? Everything I have tried seems to break
everything, and it's getting late and I'm not thinking too clearly.
Thanks in advance,
Vinny

If you want to make sure the username is unique in users table there are
several ways to achieve that:
1) Make the username column a unique key and try to catch error number 1062
(Duplicate entry for key #) when inserting new record.

$query = mysql_query("INSERT INTO users ( username, link ) VALUES
('$un','$ln')");
if (mysql_errno() == 1062) {
die("User already exists.");
} elseif (mysql_error()) {
die("Invalid query: " . mysql_error());
}

2) Do a select first and compare with the input username, then do insert.
$num = mysql_query("select users where username='$un'");
if (mysql_num_rows($num) > 0) {
die("User already exists.");
}
$query = mysql_query("INSERT INTO users ( username, link ) VALUES
('$un','$ln')");

Method #1 saves one query, and it sounds quite a practical way to manage
users with unique username.

> $result = mysql_query("SELECT link FROM links WHERE ID=$ln") or
> die("Invalid query: " . mysql_error());
Since I don't see you have insert new record for links table before this
statement, I assume you won't get anything from it unless you did insertion
somewhere else.

Bryan

"Vinny Gullotta" <vinny@wifidirect.com> wrote in message
news:fYoPb.49990$OM2.12074421@news4.srv.hcvlny.cv. net...
> I have this code:
>
>
> if (isset($_GET['un']) AND isset($_GET['ln'])){
>
> $un = $_GET['un'];
> $ln = $_GET['ln'];
>
> $query = mysql_query("INSERT INTO users ( username, link ) VALUES
('$un',
> '$ln')");
>
> if(!$query) die("Invalid query: " . mysql_error());
>
> $result = mysql_query("SELECT link FROM links WHERE ID=$ln") or
> die("Invalid query: " . mysql_error());
>
> $y = mysql_fetch_array($result);
>
> $go_link = $y['link'];
>
> header("Location: $go_link");
>
> exit();
>
> }else{
> echo "The required criteria was not found in the link.";
>
> }
>
>
>
>
> I need to write an IF statement that will only add $un and $ln to the
table
> users if the last one added was not the same username as this one (if it's
> the same link, that's ok). For the ELSE part, it should still forward them
> on to $go_link. Can anyone help? Everything I have tried seems to break
> everything, and it's getting late and I'm not thinking too clearly.
> Thanks in advance,
> Vinny
>
>

On 2004-01-25, Bryan Chan <lestatc@go.com> wrote:

> If you want to make sure the username is unique in users table there are
> several ways to achieve that:

> Do a select first and compare with the input username, then do insert.
> $num = mysql_query("select users where username='$un'");
> if (mysql_num_rows($num) > 0) {
> die("User already exists.");
> }
> $query = mysql_query("INSERT INTO users ( username, link ) VALUES
> ('$un','$ln')");

This solution has concurrency problems.


--
http://home.mysth.be/~timvw

On 2004-01-21, Vinny Gullotta <vinny@wifidirect.com> wrote:
> I need to write an IF statement that will only add $un and $ln to the table
> users if the last one added was not the same username as this one (if it's
> the same link, that's ok).

Point your browser at the manual at mysql.com

Lookup how to lock a table / do transactions
Lookup what LAST_INSERT_ID returns.


--
http://home.mysth.be/~timvw