I have a decimal field (ie field_testing) with precision = 10 and scale = 8. I need to change the precision to 11. I was planning on writing a migration script that does the following:

  • Update field_config row with field_name = 'field_testing' -- set the 'precision' field to 11.
  • Alter the field_testing table structure to adjust the precision of the 'field_testing_value' field to 11.

Few questions related to this:

  1. Given that I run this while in maintenance mode, is this safe to do?
  2. Is there anything else I need to do? The default values is and will still be blank, so changes need to go into field_config_instance, I think.

Thanks, Larry

2 Answers 2


Larry, On the Drupal side, those are the only changes you need to make, the field_config_instance table doesn't track the data specifications. Just don't forget to clear the cache_field table, and the MySQL tables themselves too.


Just changing the field data and field data revisions tables does not appear to be all that is needed.

I went through this and ran drush cc all when I go to:

/admin/structure/types/manage/company/fields/field_[rest of field name]

I am presented with the old precision value still. It appears field_config also needs to be updated but I am not sure how to best change the data column. This appears to be a better solution which I have not implemented yet.

trying to change field type through sql: Notice: Undefined index: precision in number_field_schema()

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