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

mysql sql database
Michael picture Michael · May 10, 2011 · Viewed 1.4M times · Source 
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

Felipe Buccioni picture Felipe Buccioni · May 10, 2011 
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.

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