Build sql statement based on form input

[j_70]

I am trying to build a sql statement based on form input. I want the where clause to reflect only those values that have been filled in.

So:

$id='1';
$category='Oracle Server';

$sqlstatements = array(1=>$id, 2=>$category);
ksort($sqlstatements);

while (list($value,$Elements) = each($sqlstatements)){
[I]This is where I would like to build the sql statement listed below[/I]
}

select a., b.
from books a, authors b
where a.author1=$id
and category=$category;

I am having problems getting the where / and sequence right. Is this how others build these sql statements?

[bogu]

I do it something like this:

$cond = "1";
if (!empty($id)) $cond.= " AND a.author1={$id}";
if (!empty($category)) $cond.= " AND category='{$category}'";

$sql = "select a.*, b.* ";
$sql.= "from books a, authors b ";
$sql.= "where {$cond}";