How do i create an inner join between two fields

class DRS(models.Model):
    _inherit = "product.template"
    # BASIC INFORMATION
    supplier = fields.Char()
    product_name_eng = fields.Char()
    product_name_chi = fields.Char()
    product_category = fields.Char()
    brand_name_eng = fields.Char()
    brand_name_chi = fields.Char()
    sup_product_code = fields.Char()
    drs_product_code = fields.Char()
    mlt = fields.Integer()
    allergy_warning = fields.Boolean()
    product_material_percentage = fields.Char()
    product_link = fields.Char()
    # COMPLIANCE INFORMATION
    countryoforigin = fields.Char()
    medicaldevice = fields.Boolean()
    wireless = fields.Char()
    otherwireless = fields.Char()
    hscode = fields.Char()
    importexport = fields.Char()
    containmaterial = fields.Char()
    potentialhazards = fields.Char()
    # OTHER
    notes = fields.Text()

    # REFERENCE INFORMATION
    refinfo_id = fields.One2many('drs_product_views.refinfo',
                                 'drs_product_code', string="Reference Info")


class refinfo(models.Model):
    _name = 'drs_product_views.refinfo'

    drs_product_code = fields.Many2one('product.template',
                                        ondelete='cascade', string="Product")

    file = fields.Char()
    link = fields.Char()
    type = fields.Char()
    appliedVariationProduct = fields.Char()
    applicableRegion = fields.Char()
    description = fields.Text()