Mysql：如何在插入时将正值转换为负值

I have one table transaction with columns (id, amount) all positive integers and I have another table refund with same columns but here amount is expected to be negative. Now I want to use Insert into command to select from transaction and insert into refund. How can I make the amount negative while inserting. following is the query that I am trying.I have one table transaction with columns (id,