Re: Document atthasmissing default optimization avoids verification table scan

Coming back to this after a respite I think the tip needs to be moved just like everything else.  For much the same reason (though this may only be a personal bias), I know what SQL Commands do the various things that DDL encompasses (especially the basics like adding a column) and so the DDL section is really just a tutorial-like chapter that I will generally forget about because I will go straight to the official source which is the SQL Command Reference.  My future self would want the tip to show up there.  If we put the tip after the existing paragraph that starts: "Adding a column with a volatile DEFAULT or changing the type of an existing column..." the need to specify an example function in the tip goes away - though maybe it should be moved to the notes paragraph instead: "with a volatile DEFAULT (e.g., clock_timestamp()) or  changing the type of an existing column..."

David J.