cockroachDB postgreSQL的array_position没找到的话返回NULL

array_position(days,:day) is null

function signinAppend($param,&$arr,$token,$ui){
    $dbh = new PDO(CRDB, CRDB_U, CRDB_P, array(
        PDO::ATTR_ERRMODE          => PDO::ERRMODE_EXCEPTION,
        PDO::ATTR_EMULATE_PREPARES => true,
        PDO::ATTR_PERSISTENT => true
    ));
    try{
        $keys = ["year","month","day"];
        if(checkParam($keys,$param)){
            $year = $param["year"];
            $month = $param["month"];
            $day = (int)$param["day"];
        }else{
            $year = Date("Y");
            $month =  Date("m");
            $day =  (int)Date("d");
        }

        try {
            $dbh->beginTransaction();
            $dbh->exec("SAVEPOINT cockroach_restart_signin");// This savepoint allows us to retry our transaction.
        } catch (Exception $e) {
            $arr["msg"] = "signinAppend transation开始失败";
            return;
        }
        $n = 0;
        $maxretry = 3;
        while (true) {
            try {
                if($n++ > $maxretry){
                    throw new Exception("transation重试次数超标");
                }
                $stmt = $dbh->prepare('select id from signin WHERE userid=:userid and year=:year and month=:month');
                $stmt->bindValue(':userid', $ui["id"], PDO::PARAM_INT);
                $stmt->bindValue(':year', $year, PDO::PARAM_INT);
                $stmt->bindValue(':month', $month, PDO::PARAM_INT);
                $stmt->execute();
                if ($stmt->rowCount() <= 0) {//没有该月份数据，插入。
                    $arr["msg"] = "签到成功";
                    $stmt = $dbh->prepare(
                        'insert into signin(userid,year,month,days) values(:userid,:year,:month,:day)'
                    );
                    $stmt->bindValue(':userid', $ui["id"], PDO::PARAM_INT);
                    $stmt->bindValue(':year', $year, PDO::PARAM_INT);
                    $stmt->bindValue(':month', $month, PDO::PARAM_INT);
                    $stmt->bindValue(':day', '{'.$day.'}', PDO::PARAM_STR);
                    $stmt->execute();
                    if($stmt->rowCount() <=0){
                        throw new Exception("测试异常2");
                    }
                }else{
                    $arr["msg"] = "签到成功";
                    $stmt = $dbh->prepare(
                        'update signin set days=array_append(days,:day) where userid=:userid and year=:year and month=:month and array_position(days,:day) is null'
                    );
                    $stmt->bindValue(':day', $day, PDO::PARAM_STR);   
                    $stmt->bindValue(':userid', $ui["id"], PDO::PARAM_INT);
                    $stmt->bindValue(':year', $year, PDO::PARAM_INT);
                    $stmt->bindValue(':month', $month, PDO::PARAM_INT);
                    $stmt->execute();
                    if ($stmt->rowCount() <= 0) {//没有该月份数据，插入。
                        $arr["msg"] = "重复签到";    
                    }
                }
                $dbh->exec('RELEASE SAVEPOINT cockroach_restart_signin');// Attempt to release the savepoint (which is really the commit).
                $dbh->commit();
                $arr["status"] = 1;
                break;
            }catch(Exception $e0){
                $dbh->rollBack();
                $arr["msg"] = $e0->getMessage();
                return;  
            }catch (PDOException $e) {
                if ($e->getCode() != '40001') {// Non-recoverable error. Rollback and bubble error up the chain.
                    $dbh->rollBack();
                    $arr["msg"] = "userRegister error 2";
                    return;   
                } else {// Cockroach transaction retry code. Rollback to the savepoint and restart.
                    $dbh->exec('ROLLBACK TO SAVEPOINT cockroach_restart_signin');
                }
            }
 
        }
    }catch(Exception $e){
        $arr["msg"] = $e->getMessage();
    }
}