_sql_constraints = [
        (
            'identification_id_len_check',
            'check (LENGTH(identification_id) = 11)',
            ('identification_id should be 11 symbols')
        ),
    ]

Hi,

If it is not mandatory to for _sql_constraints, try to achieve the same using the constrains.

@api.constrains('identification_id')
def check_identification_id(self):
    for rec in self:
        if len(rec.identification_id) != 11:
            raise ValidationError(_('Must be 11 Characters'))

See : How To Add Constrains For A Field in Odoo12

Thanks