sql determines whether a field is empty

Determine whether a certain field in sql is NULL

<span style="color: #000000">public function dataNull($id){
        $sql = 'SELECT * FROM `vvt_company_funcs_user` WHERE ISNULL(`last_login_time`) AND id ='. $id;
        $res = $this->query($sql);
        return $res;
    }
    </span>

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