I've encountered the same problem and changing the size of data type really helps using select tools! thank you for the solution. Thank god we have this community, so i do not have to scratch my head till it turn bald haha
We started getting this error when we upgraded to 2020.3.8. It wasn't present before this version and the solution is to just use Auto Field tool at the end of every workflow. It's better than select because it will automatically take care of all text fields. As a general practice, I put Auto Field tools at the start and end of all of my workflows to minimize data set size.
This problem still exists as of May 2021. Autofield saved a lot of time, and i manually shortened the length of all of the string fields, and then the write to SQL went smoothly. Before that, though, it was a series of seemingly random errors, trying to write some fields, then other fields and getting non-specific error messages which didn't enlighten me OR solve the problem. The Thrill of Solving, indeed!
Thanks to the community for lightening the load, again. Alteryx is a big complicated tool that can do everything, and usually someone knows how to do anything you can think of, but connecting those facts to achieve a solution is often fairly magical. I really appreciate everyone sharing their expertise and experience. Thank you.