At vælge den rigtige værdi

Fandt selv en løsning på problemet:

// SELET ALL PRICES
    $result = mysql_query("SELECT * FROM Listen ORDER BY date") or die(mysql_error()); 
   
// keeps getting the next row until there are no more to get (AND PUT IN ARRAY'S)
    $i=0;
    while($row = mysql_fetch_array( $result )) {

//Count number of dates;
        $i=$i+1;

//Assign mysql data to arrays
        $id[$i]=$row['id'];
        $dates[$i]=$row['date'];
      $pris1[$i]=$row['pris1'];
      $pris2[$i]=$row['pris2'];
      $pris3[$i]=$row['pris3'];
        }
       
//Set number of dates:
        $NumerOfDates=$i;
       
//Close Database
    mysql_close();
   
       
    $TargetDate=$_GET['date'];
 

        $DateIsNumber=0;
   
    //Write Target date
   
    // Find date date that is larger than the value (first date first)
        for ( $i = 1; $i <= $NumerOfDates; $i = $i+1) {
            if ($TargetDate>=$dates[$i]) {$DateIsNumber=$i;}
        }
    // if no date is found set date as first date
        if ($DateIsNumber==0) {$DateIsNumber=1;}
        echo "pris.dato: ".$dates[$DateIsNumber]."<br>";