[IMPALA-7255] Incorrect result rounding midpoint negative numbers to negative precision

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Duplicate
• Epic Color: ghx-label-2
• Assignee: Unassigned
• Reporter: Ian Cook
• Created: 06/Jul/18 11:57
• Updated: 11/Jul/18 23:23
• Resolved: 11/Jul/18 23:23

Description

Based on the Impala docs and on the behavior of other SQL engines, it's evident that:

round(-15, -1) should return -20
round(-150, -2) should return -200

and so on, because negative values at the midpoint between the upper and lower rounded values are supposed to round to the value farther from zero. However, in Impala:

round(-15, -1) returns -10
round(-150, -2) returns -100

and so on. This issue affects cases where both arguments are negative and the number being rounded is at the midpoint. I believe this issue affects cases where the first argument has any of the integer data types or the FLOAT or DOUBLE type, but not when it has a DECIMAL type. This issue seems to occur regardless of whether the numbers being rounded are specified as literals, column references, or expressions.

To reproduce this, execute queries like:

SELECT round(-15, -1);
SELECT round(-150, -2);
SELECT round(cast(-150 AS BIGINT), -2);
SELECT round(cast(-150 AS DOUBLE), -2);

Issue Links

• duplicates: IMPALA-6468 Round() is inconsistent for Decimal and Double