[HIVE-15331] Decimal multiplication with high precision/scale often returns NULL

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.2.0
• Component/s: Types

Release Note

The resulting precision/scale of decimal arithmetic has been changed in the case where the precision/scale exceeds the maximum precision of 38.

When reducing the precision/scale down to the Hive limit of 38, the new behavior is to reduce the scale to preserve the integer portion of the precision, while leaving a minimum of 6 digits for the scale.

The previous behavior was to always shrink the integer portion of the precision first before the scale.

• Assignee: Jason Dere
• Reporter: Jason Dere
• Created: 01/Dec/16 19:08
• Updated: 01/Aug/23 09:51
• Resolved: 21/Dec/16 18:07

Description

create temporary table dec (a decimal(38,18));
insert into dec values(100.0);

hive> select a*a from dec;
OK
NULL
Time taken: 0.165 seconds, Fetched: 1 row(s)

Looks like the reason is because the result of decimal(38,18) * decimal(38,18) only has 2 digits of precision for integers:

hive> set hive.explain.user=false;
hive> explain select a*a from dec;
OK
STAGE DEPENDENCIES:
  Stage-0 is a root stage

STAGE PLANS:
  Stage: Stage-0
    Fetch Operator
      limit: -1
      Processor Tree:
        TableScan
          alias: dec
          Select Operator
            expressions: (a * a) (type: decimal(38,36))
            outputColumnNames: _col0
            ListSink

Time taken: 0.039 seconds, Fetched: 15 row(s)

Issue Links

• is blocked by: HIVE-15334 HIVE-13945 changed scale rules for division
• is related to: HIVE-27553 After upgrading from Hive1 to Hive3, Decimal computation experiences a loss of precision
• is related to: SPARK-22036 BigDecimal multiplication sometimes returns null
• links to: https://reviews.apache.org/r/54505/