query.py

from django.db.models import Case, Value, When, F
from django.db.models.functions import Cast

result = (
  Live
    .objects
    .annotate(
      like_frequence=Case(
        When(like__gt=0, then=Cast('unlike', models.DecimalField()) / F('like')),
        default=Value(0),
        output_field=models.DecimelField()
      )
    )
    .filter(like_frequence__lt=0.2)
)