[simonw]

"Obviously you can kinda emulate it by adding the columns you want to cover to the key"

Right, that seems like a good solution to me.

[masklinn]

It’s a workaround, but it bloats the interior pages of the index with the covering data, which increases the size of the index and makes lookup less efficient (as they have to traverse more interior pages, and since there are more pages those are less likely to remain in cache).