“Hive” max column value from multiple columns - sql

Question

Hi: I have a situation where I need to find the max value on 3 calculated fields and store it in another field, is it possible to do it in one SQL query? Below is the example
SELECT Income1 ,
Income1 * 2% as Personal_Income ,
Income2 ,
Income2 * 10% as Share_Income ,
Income3 ,
Income3 * 1% as Job_Income ,
Max(Personal_Income, Share_Income, Job_Income )
From Table
One way I tried is to calculate Personal_Income, Share_Income, Job_Income in the first pass and in the second pass I used
Select
Case when Personal_income > Share_Income and Personal_Income > Job_Income
then Personal_income
when Share_income > Job_Income
then Share_income
Else Job_income as the greatest_income
but this require me to do 2 scans on a billion rows table, How can I avoid this and do it in a single pass? Any help much appreciated.

Answer 1

As of Hive 1.1.0 you can use greatest() function. This query will do in a single table scan:
select Income1 ,
Personal_Income ,
Income2 ,
Share_Income ,
Income3 ,
Job_Income ,
greatest(Personal_Income, Share_Income, Job_Income ) as greatest_income
from
(
SELECT Income1 ,
Income1 * 2% as Personal_Income ,
Income2 ,
Income2 * 10% as Share_Income ,
Income3 ,
Income3 * 1% as Job_Income ,
From Table
)s
;