This is a pretty commonly asked question. The answer is two fold:
1. putting the comma before doesn't actually make commenting out columns easier - it just moves the problem to the other end of the list. Just try commenting out `first_name` in your example and you'll see what I mean.
2. because normal convention would be for the comma to come immediately after an item in written English.
1. putting the comma before doesn't actually make commenting out columns easier - it just moves the problem to the other end of the list. Just try commenting out `first_name` in your example and you'll see what I mean.
2. because normal convention would be for the comma to come immediately after an item in written English.