Custom relationship or populate filed from database

I have a custom field that I put into the accounts table.
I’m trying to find a way to populate it based on data in another table (not in a module)
I’ve tried triggers but I can’t get anything to work.
Any ideas? Is this even possible?

I had the same requirement in the past and the only way I was able to make it work was to create a new module for the data I needed to use. I created the new module and unchecked the “Navigation Tab” checkbox. I made sure the fields matched up with the fields in the table I was trying to use. After deploying the module, I imported the data manually through MySQL workbench into the new module’s table.

After that, just add a related field in the accounts module.

Thanks. That got me going in the right direction. I was getting confused with the table Relationship types. Once I got that I actually went with a few db triggers to get the data to move around the way I needed it to.

If your request is about populating that custom field following determined rules, I suggest you use a logic-hook (http://urdhva-tech.blogspot.cl/2013_02_01_archive.html) or a custom program linked to SuiteCRM vía Scheduled Task (http://www.fastcomet.com/tutorials/suitecrm/manage-scheduler).
If you want to populate it every time the field is used, perhaps you should try using a relate field as stated in http://developer.sugarcrm.com/2011/08/31/howto-using-a-relate-field-to-populate-a-custom-field