After some digging, I managed to successfully copy history and trends from one item to another.
The sort of syntax I used is this:
INSERT INTO history (`itemid`, `clock`, `value`, `ns`)
SELECT '<new_itemid>', `clock`, `value`, `ns`
WHERE itemid = <old_itemid>;
INSERT INTO trends (`itemid`, `clock`, `num`,...
Column < Row < Block < Table
One column had a number, date, string, or a small number of other possibilities. It takes a few bytes or many bytes.
One row like you described (4 columns each taking a few bytes) will take perhaps 40 bytes when you add in some overhead.
One block is 16KB and holds (in your case) a few hundred rows. I mention a block ...
You can use a data modifying common table expression:
with deleted as (
DELETE FROM some_table
WHERE id = 42
INSERT INTO other_table(user_id, "timestamp")
select user_id, timestamp '2020-01-04 21:32:34'