Description:
------------
The prepared statement in PDO seems to lost or to have its type altered.

When typing a 'SELECT COALESCE(MAX(field),0) FROM table' under postgresql shell, no problem.
When using this query as is in PHP (with PDO), no problem.
When trying SELECT COALESCE(MAX(?),0) FROM table as a prepared statement, the execution fails.

Replacing "MAX(?),0" by "MAX(?),'0'" solves the problem, but the returned value is a string, and not an integer.



Reproduce code:
---------------
$stmt = $dbh->prepare("SELECT COALESCE(MAX(?),0) FROM board");
$stmt->bindParam(1,$fld);
$fld = "id_board";
if(!$stmt->execute()) print_r($stmt->errorInfo());

Expected result:
----------------
The expected result is "0" , in the case or the table is empty or the number of lines in the table.

Actual result:
--------------
The statement->errorInfo() returns : 
Array
(
    [0] => 42804
    [1] => 7
    [2] => ERREUR:  Les COALESCE types text et integer ne peuvent pas correspondre
)

In english : "the COALESCE types text and interger can't match".