Added comment syntax for single variable mysql call`

[justin-gooch]

I think this is the area a lot of people run into confusion with and it would be massively helpful to let people know about it since I personally was thrown off for the entirety of a year for it and allowed my security to lack because of it.

[petdance]

This looks great. If it's caught you up before, then I'm sure others will run into it, too.

Can you please update to explain why you have to have that extra comma there?