$row->{'inuse'} = $dbh->selectrow_array("SELECT COUNT(*) FROM Person WHERE Account_idAccount = ? AND JSON_EXISTS(custom, ?)", undef, $account, "$." . $row->{'name'});

##</code><code>##

$row->{'inuse'} = $dbh->selectrow_array("SELECT COUNT(*) FROM Person WHERE Account_idAccount = 35 AND JSON_EXISTS(custom, '$.test3')");

die $dbh->errstr if $dbh->err;
die $row->{'inuse'} if $row->{'inuse'};

##</code><code>##

SELECT COUNT(*) FROM Person WHERE Account_idAccount = 35 AND JSON_EXISTS(custom, '$.test3')