GROUP BY का उपयोग करें और MAX , इसे आजमाएं;)
select a.No_Registrasi, a.Nama_CTKI, b.Nama_Negara, CONCAT('RA-', MAX(substring(c.ID_Rad, 4) + 0)) AS ID_Rad, CONCAT('Lab-',MAX(substring(d.ID_Lab, 5) + 0)) AS Id_Lab
FROM tb_registrasi a
JOIN tb_negara_tujuan b
ON a.ID_Negara = b.ID_Negara
JOIN tb_radiologi c
ON a.No_Registrasi = c.No_Registrasi
JOIN tb_laboratorium d
ON a.No_Registrasi = d.No_Registrasi
GROUP BY a.No_Registrasi, a.Nama_CTKI, b.Nama_Negara
