How to add MySQL table column with a default value of another column of the existing row

Question

The current existing table looks like this:

id    number    amount    
1     123       30000.00
2     123       15000.00
3     321       45000.00
...   ...           


        

Answer 1

Virtual Column:

alter table Table1 
add allocated_amount integer GENERATED ALWAYS AS (amount) VIRTUAL;

Answer 2

It is not possible as default column. You can write a trigger and do that or add virtual column in Mysql 5.7.

OR

alter table Tab1 add allocated_amount int;  -- Add column
update Tab1 set allocated_amount= amount;   -- Set the value

Or you could create a Virtual Column:

alter table Table1 
add allocated_amount integer GENERATED ALWAYS AS (amount) VIRTUAL;