Verify sku # doesn't already exist

[Bowers007]

I am making a products database and need to make it so you can't enter the same sku number twice. Can someone please review this to see if I am on the right track. Here is my code:

 
        $sku = $_POST['sku'];
        $Company = $_POST['Company'];
        $Type = $_POST['Type'];
        $Material = $_POST['Material'];
        $Handle = $_POST['Handle'];
        $Revision = $_POST['Revision'];
        $EffDate = $_POST['EffDate'];
        $FinishBlankLengthSpec = $_POST['FinishBlankLengthSpec'];
        $TipAngleSpec = $_POST['TipAngleSpec'];

    $error = false;

// checking if entered is number format
if(is_numeric($sku)){   

        // checking if doesnt exist
        $query = mysql_query("select count(sku) from header_table where sku='{$sku}'");
        if(!@mysql_num_rows($query)){
                mysql_query("INSERT INTO header_table(sku,    

   Company,
   Type,
   Material,
   Handle,
   Revision,
   EffDate
  )
VALUES('$sku',
   '$Company',
   '$Type',
   '$Material',
   '$Handle',   

   '$Revision',
   '$EffDate'     

)");
        }else $error=2; 
}else $error=1;

if($error){
        switch($error){
                case 1: echo "Enter a number"; break;
                case 2: echo "This number already exists in the database"; break;
        }
        exit;
}  

// checking if entered is number format
if(is_numeric($sku)){   

        // checking if doesnt exist
        $query = mysql_query("select count(sku) from tipping_table where sku='{$sku}'");
        if(!@mysql_num_rows($query)){
                mysql_query("INSERT INTO tipping_table(sku, 
   Company,
   Type,
   Material,
   Handle,
   FinishBlankLengthSpec,
   TipAngleSpec
  )
VALUES('$sku',
   '$Company',
   '$Type',
   '$Material',
   '$Handle',   

   '$FinishBlankLengthSpec',
   '$TipAngleSpec'
)");
        }else $error=2; 
}else $error=1;

if($error){
        switch($error){
                case 1: echo "Enter a number"; break;
                case 2: echo "This number already exists in the database"; break;
        }
        exit;
}  

[bradgrafelman]

Just add a UNIQUE (or PRIMARY?) index on the 'sku' column and then perform the INSERT query without SELECT'ing anything. If the INSERT query fails with error number 1062 (duplicate data for key), then you know that the SKU is a duplicate.

[Bowers007]

How can I echo a error message if the data entry person tries to enter a duplicate? I did make sku unique but when I try to add a dup. it acts like it added it but it really did not put it in the database.

[bradgrafelman]

Check [man]mysql_errno/man to see if it's a duplicate. Example code snippet:

$sql = "INSERT INTO foo VALUES ('bar')";

if(!mysql_query($sql) && mysql_errno() == 1062) {
    // duplicate entry
}

I compacted the two mysql function calls into one if() statement, but you can certain spread it out in your code.

EDIT: Eh.. perhaps I compacted it too far. It would probably be better written as:

if(!mysql_query($sql)) {
    if(mysql_errno() == 1062) {
        // duplicate data
    } else {
        // other DB error
    }
} else {
    // data wasn't a duplicate and was inserted into DB
}

[Bowers007]

Where would this go in the code?