在SQL中使用PDO选择列中的一个celd

I have this situation after my SQL stament: One single column with the same result. For example, the age of all people with blue eyes and green jeans, will return me one column "age" with the result for example 50 years (because all people with this characteristics have 50), repeted as many time as there are people with this parameters in the DB.

How I can do in PDO (or SQL) to filter or to get only one result, or only one fild (50)? I try: fetchAll(PDO::FETCH_ASSOC) and fetchColumn() but both return a array or nothing

It's SQL.

SELECT age FROM people WHERE eyes='blue' AND jeans='green' LIMIT 1

Note that LIMIT part that will limit the results to only one row, which you'll be able to get with PDO's fetchColumn():

$sql = "SELECT age FROM people WHERE eyes='blue' AND jeans='green' LIMIT 1";
$age = $pdo->query($sql)->fetchColumn();