PHP undefined index error

I solved myself.
SELECT pw FROM user WHERE email=:u_mail

not
SELECT pw, name FROM user WHERE email=:u_mail
It would have been fine if I did.

Hi, nice to meet you.I don't know if I can help you, but at this stage, I'll write something I'm curious about.

Undefined index:name
I think shows that there is no key name for the $r associative array.

$ps=$db->prepare("SELECT pw FROM user WHERE email=:u_mail");
$ps->bindParam(":u_mail", $m);
$ps->execute();
if($ps->rowCount()>0){
$r = $ps-> fetch (PDO::FETCH_ASSOC);
// See if there is a $r key here
print var_export($r);

if($r['pw']===md5($p)){
$_SESSION['user'] = $r['name'];

Whether the print is displayed on the screen depends on how it is implemented.
When the var_export() result is displayed in the standard output,
Find the return value for $ps->fetch(PDO::FETCH_ASSOC);

Try it.