A field with precision 10, scale 2 must round to an absolute value less than 10^8

Question

I have a django-field total_price in postgres database with version 9.3.11.

Here is the current code for it.

total_value = models.DecimalField(decimal_places=100, default=0, max_digits=300)

I want to convert it to proper 2 decimal place. So I wrote this code

total_value = models.DecimalField(decimal_places=2, default=0, max_digits=10)

My migration file

# -*- coding: utf-8 -*-
from __future__ import unicode_literals

from django.db import models, migrations


class Migration(migrations.Migration):

    dependencies = [
        ('my_table', '0040_my_table_skipped'),
    ]

    operations = [
        migrations.AlterField(
            model_name='my_table',
            name='total_value',
            field=models.DecimalField(default=0, max_digits=10, decimal_places=2),
        ),
    ]

When I run command python manage.py migrate

It shows me this error

A field with precision 10, scale 2 must round to an absolute value less than 10^8.

Any idea what is this about ?

Answer 1

As @sivakumar-r mentioned above, it's the precision and scale issue.

Let's see how the Numeric(precision, scale) works:

Suppose, if we have a column defined with NUMERIC(10,3).

This means, we can only save 10 digits in total with 3 spaces after decimal point.

So the range you can save in this case is: +9999999.999 to -9999999.999.

One Solution Could be:

Alter table column to use type NUMERIC without the precision and scale.

This will accept up to 131072 digits before the decimal point; up to 16383 digits after the decimal point. As mentioned in postgres:11 Numeric types document.

Answer 2

Earlier you had decimal number like Number(300, 100). I think you have some data in this decimal field. Now you alter the decimal field to Number(10,2). So now you can only save max 99999999.99. But your old data is much more than this. Because earlier you can save decimal number of 300 max digits and 100 decimal places.