Mustafa Iman created HIVE-22877:

             Summary: Wrong decimal boundary for casting to Decimal64
                 Key: HIVE-22877
             Project: Hive
          Issue Type: Bug
          Components: Vectorization
    Affects Versions: 4.0.0
            Reporter: Mustafa Iman
            Assignee: Mustafa Iman

During vectorization, decimal fields that are obtained via generic udfs are 
cast to Decimal64 in some circumstances. For decimal to decimal64 cast, hive 
compares the source column's `scale + precision` to 18(maximum number of digits 
that can be represented by a long). A decimal can fit in a long as long as its 
`scale` is smaller than or equal to 18. Precision is irrelevant.

Since vectorized generic udf expression takes precision into account, it 
computes wrong output column vector: Decimal instead of Decimal64. This in turn 
causes ClassCastException down the operator chain.

Below query fails with class cast exception:

create table mini_store
 s_store_sk int,
 s_store_id string
row format delimited fields terminated by '\t'

create table mini_sales
 ss_store_sk int,
 ss_quantity int,
 ss_sales_price decimal(7,2)
row format delimited fields terminated by '\t'
insert into mini_store values (1, 'store');
insert into mini_sales values (1, 2, 1.2);
select s_store_id, coalesce(ss_sales_price*ss_quantity,0) sumsales
from mini_sales, mini_store where ss_store_sk = s_store_sk


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