Why all the complication in the first update.
```
update MyTable as dst
set val_a = src.val_a,
val_b = src.val_b,
val_c = src.val_c
from MyTable as src
where src.object_id == dst.object_id
and dst.snapshot_id == 2
and src.snapshot_id == 1
;
```
It is pretty much a direct translation from English into SQL.
For number 2 a better method (if you are using an old version of SQLite3 that does not have UPDATE FROM) would be:
```
update MyTable as dst
set (val_a, val_b, val_c) = (select val_a, val_b, val_c from MyTable where object_id == dst.object_id and snapshot_id == 1)
where snapshot_id == 2
;
```
You would only need to use multiple correlated subqueries for really ancient versions of SQLite3 that does not have row-tuples.