Another commenter showed how this works:

  SELECT a.foo
       , b.bar
       , g.zed
    FROM ...

While the comma placement may seem weird, it makes this exactly identical to the "AND" or "OR" placement in WHERE clauses, and the primary benefit is that it's easy to comment out any column except the first.

It's always easy to comment out any column except the first or last. Leading commas make it easy to comment out the last column, trailing commas make it easy to comment out the first.

Personally I don't think that optimization is worth the price. Trailing commas look nicer visually so I prefer them.

> While the comma placement may seem weird

It's not completely unconventional. Haskell is typically styled with that kind of comma usage, too. For example,

  [ 1
  , 2
  ]

  { foo = 1
  , bar = 2
  }

Coincidentally, SQL and Haskell are the only languages I know that use `--` for comments.

FWIW, Lua and AppleScript (and HyperTalk!) use(d) `--` as well.

(Edit: I think I misread “know” as “know of”; whoops.)

> I think I misread “know” as “know of”; whoops.

Don't worry about it; you didn't misread. I wasn't aware of AppleScript and HyperTalk, and though I read a bit on Lua some years ago, I either forgot or never realized that it used `--` for comments.

With the curly braces this makes a lot more sense. In SQL it offends my eyes (personal preference) but here it seems more clear.