使用联接库时，如何在codeigniter上创建别名

我尝试在查询中添加别名，这样就不会出现表不唯一的错误。

正如你所看到的，我在后面放了一个新名字'as'，但这给了我一个错误。我怎么做错了
这就是我的模型：

<?php 
class Joins_model extends CI_Model{
    private $table = 'cm_proveedor, cm_compras, cm_valuacion, cm_valuacionr, cm_nomina, cm_empleado';
    function _construct(){
       parent::Model();
    }
    function get_reg($data){
        $this->db->select('
                            cm_valuacion.tipo_r AS valR,
                            cm_valuacion.mano_obra AS valM,
                            cm_valuacion.hojalateria AS valH,
                            cm_valuacion.pintura AS valP,
                            cm_valuacion.mecanica AS valMec,
                            cm_valuacion.refaccion AS valRef,
                            cm_valuacion.shojalateria AS valSH,
                            cm_valuacion.tipo AS valT,
                            cm_valuacion.spintura AS valSP,
                            cm_valuacion.costoHojalateria AS valCH,
                            cm_valuacion.smecanica AS valSM,
                            cm_valuacion.costoPintura AS valCP,
                            cm_valuacion.costoMecanica AS valCM,
                            cm_valuacion.pv_hojalateria AS valPH,
                            cm_valuacion.pv_pintura AS valPP,
                            cm_valuacion.pv_mecanica AS valPM,
                            cm_valuacion.pc_hojalateria AS valPH,
                            cm_valuacion.pc_pintura AS valPPin,
                            cm_valuacion.pc_mecanica AS valPMec,
                            cm_compras.precio,
                            cm_proveedor.nombre,
                            cm_nomina.nomina,
                            cm_empleado.nombre,
                            cm_nomina.id_nomina_gral
                            ',FALSE);
        $this->db->from('cm_valuacion');
        $this->db->join('cm_valuacionr','cm_valuacionr.id_siniestro = cm_valuacion.id_siniestro');
        $this->db->join('cm_compras','cm_valuacionr.id_siniestro = cm_compras.id_siniestro');
        $this->db->join('cm_proveedor','cm_proveedor.id = cm_compras.id_proveedor');
        $this->db->join('cm_nomina','cm_nomina.id_siniestro = cm_compras.id_siniestro');
        $this->db->join('cm_empleado','cm_nomina.id_empleado = cm_empleado.id');
        $this->db->join('cm_nomina_gral','cm_nomina.id_nomina_gral = cm_nomina_gral.id');
        $this->db->where('cm_valuacion.id_siniestro',$data);
        //$this->db->order_by('id','asc');
        $this->db->distinct();
        return $this->db->get($this->table);
    }

}
?>

我得到的错误是：

发生数据库错误错误编号：1066不是唯一的表/别名："cm_valuacion"选择DISTINCT cm_valacion.tipo_r AS valR，cm_valusion.mano_obra AS valM，cm_val acion.hojalateria AS valH，cm_vallacion.pintura AS valP，cm_valiacion.mecanica AS valMec，cm_vvalacion.refaccion AS valRef，cm_valaacion.shojalateria AS valSH，cm_valoacion.tipo AS valT，cm_vala acion.spintura AS valSP，cm_valuacion.costoHojalateria AS valCH，cm_vualacion.smecanica AS valSM，cm_valacion.costoPintura AS valCP，cm_valusion.costoMecanica AS valCM，cm_val acion.pv_hojaleria AS valPH，cm_vallacion.pv_pintura AS valPP，cm_valiacion.pv_mecanica AS valPM，cm_valuacion.pc_hojalaria AS valPH，cm_valaacion.pc_pintura AS-valPPin，cm_vvalacion.pc_mecanicaAS-valPMec，cm_compras.precio，cm_proveedor.nombre，cm_nomina.nomina，cm_empleado.nombre，cm_nominame.id_nomina_gral FROM（cm_valuacion、cm_proveedor、cm_compras、cm_valuacion、cm_valuacionr、cm_nomina、cm_empleado）在cm_valuacionr上加入cm_valuacionr。id_siniestro＝cm_valuacion。id_siniestro在cm_valuacionr上加入cm_compras。id_siniestro＝cm_compras。id_siniestro在cm_proveedor上加入cm_proveedor。id＝cm_compras。id_proveedor在cm_nomina上加入cm_nomina。id_siniestro＝cm_compras。id_siniestro在cm_nomina上加入cm_empleado。CCD_ 30＝CCD_。id在cm_nomina上加入cm_nomina_gral。id_nomina_gral＝cm_nomina_gral。id，其中cm_valuacion。id_siniestro='6489'文件名：C:''examplep''htdocs''index''system''database''DB_driver.php线路编号：330