why created_at is greater than updated_at while inserting data in table

hello, i am using this code to update created_at and updated_at in models:

        created_at = models.DateTimeField(auto_now_add=True)

updated_at= models.DateTimeField(auto_now=True,null=True)

but however there is created _at is greater than updated_at when data is inserted: 

       created_at  -> 2018-11-26 11:11:30.020989

       updated_at -> 2018-11-26 11:11:30.019762

please help, thank you.

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