Everything works as expected on my development machine, but when deploying to quality assurance environment, tests are failing because MariaDB is padding the result set with extra precision zeros after a decimal.

For example, when I run this query:

SELECT GREATEST(  '2016-04-14 15:06:30', NOW() )

On dev, running Ubuntu 14.04.4 LTS (Trusty Tahr) mysql Ver 14.14 Distrib 5.5.47, for debian-linux-gnu (x86_64) using readline 6.3, I get this expected result:

2016-04-18 09:07:42

On test, running Red Hat Enterprise Linux Server 7.2 (Maipo) mysql Ver 15.1 Distrib 5.5.44-MariaDB, for Linux (x86_64) using readline 5.1, I get this unexpected result:

2016-04-18 09:07:42.000000

I don't see anything in the GREATEST() documentation that would explain this behavior, so I think it must be a server configuration setting in my.cnf but I couldn't find anything in online search results.

Even more curiously, when running the following queries, I get the same unpadded results on both machines:

SELECT GREATEST(  '2016-04-14 15:06:30', '2016-04-14 16:06:30' )

2016-04-14 16:06:30

SELECT GREATEST(  NOW(), NOW() )

2016-04-18 09:24:22

SELECT GREATEST(  5, 10 )

10

Why is MariaDB GREATEST() padding/appending my result set with zeros on timestamp comparison with NOW()?