[sql] SQL select everything in an array

My homework has a problem for example there is a category array $cat=array('1','4','5','7'); now i need to select products from db based on the category that is

SELECT * FROM products WHERE catid='1'
SELECT * FROM products WHERE catid='4'
SELECT * FROM products WHERE catid='5'
SELECT * FROM products WHERE catid='7'

Is it possible to do this in a single query? as the final results of the four queries will be combined.

// array of $ids that you need to select
$ids = array('1', '2', '3', '4', '5', '6', '7', '8');

// create sql part for IN condition by imploding comma after each id
$in = '(' . implode(',', $ids) .')';

// create sql
$sql = 'SELECT * FROM products WHERE catid IN ' . $in;

// see what you get
var_dump($sql);

Update: (a short version and update missing comma)

$ids = array('1','2','3','4');
$sql = 'SELECT * FROM products WHERE catid IN (' . implode(',', $ids) . ')';

$SQL_Part="("
$i=0;
while ($i<length($cat)-1)
{
   $SQL_Part+=$cat[i]+",";
}
$SQL_Part=$SQL_Part+$cat[$i+1]+")"

$SQL="SELECT * FROM products WHERE catid IN "+$SQL_Part;

It's more generic and will fit for any array!!