please solve my sql join codeigniter error

I have a problem to create Join query in codeigniter. Below is the code

 public function getKeterangan($id_kelas){
  $this->db->select('*')
        ->from('a.absensi')
        ->join('s.siswa', 'a.id_siswa = s.id_siswa')
        ->join('kelas.k', 'a.id_kelas = k.id_kelas')
        ->where('a.id_kelas.*',  'a.keterangan.*');  
  return $this->db->get()->result();
 }

And the error shown like this :

You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ‘* = ‘a.keterangan.” at line 5
SELECT * FROM a.absensi JOIN s.siswa ON a.id_siswa = s.id_siswa JOIN kelas.k ON a.id_kelas = k.id_kelas WHERE a.id_kelas. = ‘a.keterangan.*’

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Please help me to solve this.. I’m new in codeigniter

>Solution :

It looks like you have an issue with your ->where() statement in the query. You are trying to use a.id_kelas.* and a.keterangan.*, which are incorrect syntax. Instead, you should compare specific columns