query inside a query

[NoobLaPHP]

I have a select option and want to include it in my query.

$select = mysql_real_escape_string($_POST[select]);

if($fetch->where$select){

So if the select value was at 2 it would read

if($fetch->where2){
 

How would i do it? Would if($fetch->where.$select){ work putting in a . ?

 

also in the mysql 

 

mysql_query("UPDATE `table` SET `where$select`='input' ");

[NoobLaPHP]

Figured it out. I used 

$where = "where".$select;

 

if($fetch->$where){

 

mysql_query("UPDATE `table` SET `$where`='input' ");