Nice easy question that I actually got hit with recently. Code that had been running live for 11 years, someone reported it was missing a column. Went digging and saw the missing comma. Quick easy fix, but when the code is NOT formatted nicely (ie all selected columns on one line), a missing comma is INCREDIBLY difficult to find.
Thankfully tools exist (free and paid) to do code formatting and ran that and it was quickly obvious what was wrong.