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This change implements the DECIMAL_V2's behavior for AVG(). The differences with DECIMAL_V1 are: 1. The output type has a minimum scale of 6. This is similar to MS SQL's behavior which takes the max of 6 and the input type's scale. We deviate from MS SQL in the output's precision which is always set to 38. We use the smallest precision which can store the output. A key insight is that the output of AVG() is no wider than the inputs. Precision only needs to be adjusted when the scale is augmented. Using a smaller precision avoids potential loss of precision in subsequent decimal operations (e.g. division) if AVG() is a subexpression. Please note that the output type is different from SUM()/COUNT() as the latter can have a much larger scale. 2. Due to a minimum of 6 decimal places for the output, AVG() for decimal values whose whole number part exceeds 32 decimal places (e.g. DECIMAL(38,4), DECIMAL(33,0)) will always overflow as the scale is augmented to 6. Certain decimal types which work with AVG() in DECIMAL_V1 no longer work in DECIMAL_V2. Change-Id: I28f5ef0370938440eb5b1c6d29b2f24e6f88499f Reviewed-on: http://gerrit.cloudera.org:8080/6038 Reviewed-by: Dan Hecht <dhecht@cloudera.com> Reviewed-by: Alex Behm <alex.behm@cloudera.com> Tested-by: Impala Public Jenkins