In x-match I select the RA and DEC columns from my uploaded csv file in MyDB but I get the error when matching with a Datalab table "column o.ra does not exist"

Question

I have a csv file and I want to match objects from this file to a file in Datalab. I am using the Astro Data Lab - Xmatch web interface. The interface requires me to indicate the RA, DEC columns and I do - they are recognized by the interface. But then, the query fails:  "column o.ra does not exist". I do not even understand what the "o" stands for (my file is named "bulsan").