Código PHP:
$para1 = "";
$para2 = "";
$para3 = "";
$variables = "";
$go = 0;
if(!empty($para1)){
$variables .="WHERE para1='$para1'"; $go = 1;
}
if(!empty($para2)){
if($go > 0){ $variables .=" AND "; }else{ $variables .="WHERE "; }
$variables .="para2='$para2'"; $go = 2;
}
if(!empty($para3)){
if($go > 0){ $variables .=" AND "; }else{ $variables .="WHERE "; }
$variables .="para3='$para3'";
}
$sql = mysql_query("SELECT * FROM tabla $variables");
$data = mysql_fetch_array($sql);
$something = $data['something'];