Song Jun created HIVE-19294:
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Summary: grouping sets when contains a constant column
Key: HIVE-19294
URL: https://issues.apache.org/jira/browse/HIVE-19294
Project: Hive
Issue Type: Bug
Components: CBO
Affects Versions: 2.3.2
Reporter: Song Jun
We have different results between Hive-1.2.2 and Hive-2.3.2, SQL like this:
{code:java}
select
case when a='all' then 'x'
when b=1 then 'y'
else 'z'
end, c
from (
select
a,b,count(1) as c
from (
select
'all' as a,b
from test
) t1 group by a,b grouping sets(a,b)
) t2;
{code}
We have a grouping sets using the column a which is a contant value 'all' in
its subquery.
The result of Hive 1.2.2(same result when set hive.cbo.enable to true or false):
{code:java}
x 3
y 2
z 1 {code}
The result of Hive 2.3.2(same result when set hive.cbo.enable to true or false):
{code:java}
x 3
x 2
x 1{code}
I dig it out for Hive 2.3.2 and set hive.cbo.enable=false, I found it that the
optimizer
ConstantPropagate optimize the code according to the constant column value
'all' in the subquery:
{code:java}
case when a='all' then 'x'
when b=1 then 'y'
else 'z'
end
{code}
to
{code:java}
Select Operator
expressions: CASE WHEN (true) THEN ('x') WHEN ((_col1 = 1)) THEN ('y') ELSE
('z') END (type: string), _col3 (type: bigint)
outputColumnNames: _col0, _col1
Statistics: Num rows: 3 Data size: 3 Basic stats: COMPLETE Column stats: NONE
{code}
That is case when a = 'all' explained as case when (true), so we always has
the value of 'x'.
So, which should be right for the above query case?
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