PDO lastInsertID返回0

Question

I am having trouble with lastInsertID returning 0. It is working in another page, so I have something wrong here.

The following is in a try/catch block.

$idCount = "42";
/** set the database **/
$db = new PDO("mysql:host=$db_host;dbname=$db_name", $db_user, $db_pass);
/** set the error reporting attribute **/
$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);            
$stmt = $db->prepare("SELECT image1 FROM items WHERE `id` = :id");    
/** bind the parameters **/
$stmt->bindParam(':id', $idCount, PDO::PARAM_STR);   
$stmt->execute();                 
$idCount = $db->lastInsertId();
echo $idCount;

Answer 1

lastInsertId() will only return the last insert id if you actually do an insert. You are only doing a select .

Answer 2

The function name ->lastInsertId() should give you a hint that SELECT statements wouldn't normally set the last insert id.

Typically only INSERT statements on tables with an auto_increment column exhibit that behaviour.

There are exceptions though, such as when LAST_INSERT_ID(expr) is used:

SELECT LAST_INSERT_ID(`id`) AS `id`, image1 FROM items WHERE `id` = :id