Django doesn't properly migrate IntegerField(default=0)

[bedbad]

Steps To Reproduce:

1. Create a model

class AModel(models.Model):
    afield = models.IntegerField()

2. Migrate AModel into the schema
3. Change AMode:

   class AModel(models.Model):
       afield = models.IntegerField(default=0)
   

4. Observe the sql form of migration:

 python manage.py sqlmigrate app 0003

It will look like this:

UPDATE `app_amodel` SET `afield` = 0 WHERE `afield` IS NULL;
ALTER TABLE `app_amodel` MODIFY `afield` integer NOT NULL;

Expected Behaviour:

UPDATE `app_amodel` SET `afield` = 0 WHERE `afield` IS NULL;
ALTER TABLE `app_amodel` MODIFY `afield` integer NOT NULL DEFAULT 0;

[Simon Charette]

Please refer to ​the documentation about db_default.

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