'IF' in 'SELECT' statement - choose output value based on column values

Question

SELECT id, amount FROM report 

I need amount to be amount if report.type='P' and -amount if report.type='N'. How do I add this to the above query?

Answer 1

SELECT id,         IF(type = 'P', amount, amount * -1) as amount FROM report 

See http://dev.mysql.com/doc/refman/5.0/en/control-flow-functions.html.

Additionally, you could handle when the condition is null. In the case of a null amount:

SELECT id,         IF(type = 'P', IFNULL(amount,0), IFNULL(amount,0) * -1) as amount FROM report 

The part IFNULL(amount,0) means when amount is not null return amount else return 0.

Answer 2

Use a case statement:

select id,     case report.type         when 'P' then amount         when 'N' then -amount     end as amount from     `report`