David Maughan created HIVE-15328:
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Summary: Inconsistent/incorrect handling of NULL in nested structs
Key: HIVE-15328
URL: https://issues.apache.org/jira/browse/HIVE-15328
Project: Hive
Issue Type: Bug
Components: Hive
Affects Versions: 2.1.0
Reporter: David Maughan
h2. Overview
Performing {{IS NULL}} checks against a null struct that is generated as part
of a UDF correctly returns {{true}}. However, the same check against the same
null struct that has been persisted to a table incorrectly returns {{false}}.
Additionally, when a child field of the null struct is inspected in the same
query, the result of the null check on the struct itself reverses itself to
{{true}}.
The issue does not appear to be dependent on the storage format of the table as
the same result is repeated with TEXTFILE, PARQUET, ORC and AVRO.
h2. Example
In this example I have used {{if(1=1, null, named_struct('c', 1)}} as a crude
method of generating a simple null struct.
h4. 'b' is correctly reported as {{true}}.
{code}
hive> select
> b is null,
> b
> from (
> select
> if(1=1, null, named_struct('c', 1)) as b
> ) as a;
OK
true NULL
{code}
h4. 'b' is correctly reported as {{true}} when also inspecting 'b.c'.
{code}
hive>
> select
> b is null,
> b.c is null,
> b
> from (
> select
> if(1=1, null, named_struct('c', 1)) as b
> ) as a;
OK
true true NULL
{code}
h4. Persist the data to a table
{code}
hive>
> create table a
> as
> select
> if(1=1, null, named_struct('c', 1)) as b;
OK
{code}
h4. 'b' is incorrectly reported as {{false}}.
{code}
hive>
> select
> b is null,
> b
> from a;
OK
false NULL
{code}
h4. 'b' is now correctly reported as {{true}} when also inspecting 'b.c'.
{code}
hive>
> select
> b is null,
> b.c is null,
> b
> from a;
OK
true true NULL
{code}
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