# Saving results of sum method into another column? **URL:** \ **Category:** Rails\ **Created:** [January 16, 2009, 1:07pm UTC](https://www.ruby-forum.com/t/saving-results-of-sum-method-into-another-column/157901 "2009-01-16T13:07:27Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![herman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/eada6e/32.png) [@herman](https://www.ruby-forum.com/u/herman)\ **Post date:** [January 16, 2009, 1:07pm UTC](https://www.ruby-forum.com/t/saving-results-of-sum-method-into-another-column/157901/1 "2009-01-16T13:07:27Z")
Basically what I’m trying to do is get the sum of 2 columns and save those results in another. I guess I’m looking to do something like this: a = Product.find(:all) b = Product.sum(“test + test2”, :group =\> “id”) a.test3 = b a.save Obviously that doesn’t work, but I’m trying to achieve something like that. Any suggestions? ---
**Author:** ![herman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/eada6e/32.png) [@herman](https://www.ruby-forum.com/u/herman)\ **Post date:** [January 16, 2009, 1:20pm UTC](https://www.ruby-forum.com/t/saving-results-of-sum-method-into-another-column/157901/2 "2009-01-16T13:20:24Z")
On 16 Jan 2009, at 10:19, Herman wrote: > that. Any suggestions? Product.update “test3 = test+test2” would probably do it. Fred ---
**Author:** ![herman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/eada6e/32.png) [@herman](https://www.ruby-forum.com/u/herman)\ **Post date:** [January 16, 2009, 7:42pm UTC](https://www.ruby-forum.com/t/saving-results-of-sum-method-into-another-column/157901/3 "2009-01-16T19:42:05Z")
On 16 Jan 2009, at 16:34, Herman wrote: > That didn’t work. I received: ArgumentError: wrong number of arguments > (1 for 2) > > I tried something like this and it also didn’t work: > Product.update\_all(“test3”, :sum =\> “test”+“test2”, :group =\> “id”) oops, typo, should be Product.update\_all “test3 = test+test2” ---
**Author:** ![herman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/eada6e/32.png) [@herman](https://www.ruby-forum.com/u/herman)\ **Post date:** [January 16, 2009, 5:35pm UTC](https://www.ruby-forum.com/t/saving-results-of-sum-method-into-another-column/157901/4 "2009-01-16T17:35:07Z")
That didn’t work. I received: ArgumentError: wrong number of arguments (1 for 2) I tried something like this and it also didn’t work: Product.update\_all(“test3”, :sum =\> “test”+“test2”, :group =\> “id”) I’d imagine I’m not that far off, but I can’t figure it out. On Jan 16, 6:19 am, Frederick C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![herman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/eada6e/32.png) [@herman](https://www.ruby-forum.com/u/herman)\ **Post date:** [January 17, 2009, 9:37pm UTC](https://www.ruby-forum.com/t/saving-results-of-sum-method-into-another-column/157901/5 "2009-01-17T21:37:48Z")
Just to give another perspective… Do you really need to save the sum? Could it be calculated whenever you need it? If you save the sum you need to be confident that nothing will cause your data to get out of sync, such as some update to ‘test’ that does not update the sum. If you decide you do want to save the sum, could the database management system handle it for you? E.g. in PostgreSQL you can define triggers - in this case a trigger could update the sum for you no matter how ‘test’ and ‘test2’ are updated. You’d then have much greater faith in the reliability of each sum. ---
**Author:** ![herman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/eada6e/32.png) [@herman](https://www.ruby-forum.com/u/herman)\ **Post date:** [January 16, 2009, 9:31pm UTC](https://www.ruby-forum.com/t/saving-results-of-sum-method-into-another-column/157901/6 "2009-01-16T21:31:25Z")
Works great. Thank you so much! On Jan 16, 12:41 pm, Frederick C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)