[IMPALA-4738] stddev_samp() returns 0 when it should return NULL

• Type: Bug
• Status: Resolved
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: Impala 2.8.0
• Fix Version/s: Impala 2.9.0
• Component/s: Backend
• Labels: correctness
• Assignee: Anuj Phadke
• Reporter: Greg Rahn
• Created: 06/Jan/17 18:32
• Updated: 07/Feb/17 17:28
• Resolved: 07/Feb/17 17:24

Description

Discovered using SF1 TPC-DS and query17.

PostgreSQL 9.6.1

grahn=# select stddev_samp(56);
 stddev_samp
-------------
        NULL
(1 row)

Impala version 2.7.0-cdh5.10.0 RELEASE (build 1c57740759e175d8810c6790af3c5a60862a0ce9)

select stddev_samp(56) from (values(1)) t;
+-----------------+
| stddev_samp(56) |
+-----------------+
| 0               |
+-----------------+