$result equals nothing if mysql column not found?

How could i get $result to开发者_JAVA百科o equal nothing if the column doesn't exist in PHP?

I was thinking something like this:

$result=mysql_query("SELECT * FROM users WHERE username=$key DESC LIMIT 1")or die ($result = '');

But i was told thats wrong.

It's wrong because you're killing the script with die when a DB error occurs, rather than doing stuff when you find no row.

What you presumably need is more like:

$result = mysql_query($query);
if ($result) {
  if ($row = mysql_fetch_assoc($result)) {
    // do stuff with row
  } else {
    // do stuff without row
  }
} else { // not needed but left here for illustration purposes
  // this is the part that would occur, had you called mysql_query(...) or die;
  die(mysql_error());
}

$result=mysql_query("SELECT * FROM users WHERE username= '$key' LIMIT 1")or die (mysql_error());

then check the result of mysql_num_rows()

If you mean that the result returns 0 rows, you can check with mysql_num_rows, like this:

$result=mysql_query("SELECT * FROM users WHERE username=$key DESC LIMIT 1");
if (mysql_num_rows($result) == 0)
    $result = '';

Your code will set $result to '' if there's an error, in which case mysql_query returns false. It will also halt the code, since you're calling die(). An empty result set is not an error, however. In that case mysql_query returns a valid resource identifier with no rows. If I understand your question, this is what you want to do:

$result=mysql_query("SELECT * FROM users WHERE username=$key DESC LIMIT 1");

if (mysql_num_rows($result) == 0){
    $result = '';
}

<?php
    // Here I assume you're using PHP PDO
    $pdo = new PDO("mysql:server=localhost;dbname=mydatabase", "root", "");
    $result = $pdo->query("SELECT * FROM users WHERE username=$key DESC LIMIT 1");
    $errorcode = $pdo->errorCode();
    $errorinfo = $pdo->errorInfo();

    // Columns doesn't exist
    if($errorcode == "43072") $result = "";

    // Other error...
    else if($errorcode != "00000") die("MySQL Error: " . $errorinfo[2]);
?>