Add Remove The Default Value On A Column as a rails til

rails/remove-the-default-value-on-a-column.md

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+# Remove The Default Value On A Column
+
+You have a column on one of your database tables with a default value. You'd
+like to remove the default value. Removing the default is the same as
+setting it to `nil`. You can do this with the ActiveRecord DSL using the
+`change_column_default` method.
+
+```ruby
+def change
+  change_column_default :users, :age, nil
+end
+```
+
+See [the
+docs](http://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/SchemaStatements.html#method-i-change_column_default)
+for more details.