'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

Answer 1

Most simplest way is to use a IF(). Yes Mysql allows you to do conditional logic. IF function takes 3 params CONDITION, TRUE OUTCOME, FALSE OUTCOME.

So Logic is

if report.type = 'p' 
    amount = amount 
else 
    amount = -1*amount 

SQL

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

You may skip abs() if all no's are +ve only