How to transfer value by sql query?

Question

MySQL

There are 2 tables, the structure is the same, the fields are slightly different:
The first table. 2 id columns | num
Second table. 2 id columns | numold
New value num arrives. Task: get the value num from the first table and transfer it to numold of the second table. After that, first enter a new value in num.

Answer 1

BEFORE UPDATE trigger on the first table.