Update values to negative based on another column

Question

I have a table that contains sales invoices and credit notes, both are held in the table as positive values.

I want to select the data and in the select statement change the credit note vales to be negative based on another column.

Any ideas?

Updated with added information

Key          Description            Type          Amount
--------------------------------------------------------
1            Invoice for 345         1             200
2            Invoice for 346         1             250
3            Invoice for 347         1             280
4            Credit  for 347         2             200
5            Invoice for 345         1             400
6            Credit note zz665       2             380

Desired result from select

Key          Description            Type          Amount
--------------------------------------------------------
1            Invoice for 345         1             200
2            Invoice for 346         1             250
3            Invoice for 347         1             280
4            Credit  for 347         2            -200
5            Invoice for 345         1             400
6            Credit note zz665       2            -380

thanks a lot, i have playing around with ABS but i cant figure out the exact usage to get my desired output.

Answer 1

I am assuming that when type = 1, then positive and when type = 2 then negative. If the type could include more values you will have to amend the case statement because everything other than 1 will be negative.

select
  key
, description
, type
, case
   when type = 1 then amount
  else
   amount * -1
  end as amount