That's a pretty long commit message.
The summary is that we can now, using single command, do insert/update/delete with some sanity checking – which can, to some extent, simplify, or maybe even optimize certain operations like loading data to existing datasets.
Let's see the example shown in commit message, with some sensible-ish data.
row (sid, delta) (1,10) got matched (there is target row with tid = 1), but delta >= balance, so the row in target was removed.
All in all – it looks very powerful, and will allow easier writing of certain data transformations.
Despite the fact that this feature is not yet fully complete (partitioning, returning, updateable views), it is definitely a great addition. Thanks a lot.
Unfortunately, Simon Riggs has reverted his patch !