~~~ UPDATE MyTable SET (val_a,val_b,val_c) = (SELECT x.val_a, x.val_b, x.val_c FROM MyTable AS x WHERE x.snapshot_id=1 AND x.object_id=MyTable.object_id) WHERE snapshot_id=2 ~~~
~~~ UPDATE MyTable SET (val_a,val_b,val_c) = (SELECT x.val_a, x.val_b, x.val_c FROM MyTable AS x WHERE x.snapshot_id=1 AND x.object_id=MyTable.object_id) WHERE snapshot_id=2 ~~~