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https://issues.apache.org/jira/browse/HIVE-9303?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14281010#comment-14281010
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Skye Wanderman-Milne commented on HIVE-9303:
--------------------------------------------
That's my understanding. The same thing happens if you insert NULL into the
Parquet table directly too, it's not just a problem with CTAS or reading from
text.
> Parquet files are written with incorrect definition levels
> ----------------------------------------------------------
>
> Key: HIVE-9303
> URL: https://issues.apache.org/jira/browse/HIVE-9303
> Project: Hive
> Issue Type: Bug
> Affects Versions: 0.13.1
> Reporter: Skye Wanderman-Milne
>
> The definition level, which determines which level of nesting is NULL,
> appears to always be n or n-1, where n is the maximum definition level. This
> means that only the innermost level of nesting can be NULL. This is only
> relevant for Parquet files. For example:
> {code:sql}
> CREATE TABLE text_tbl (a STRUCT<b:STRUCT<c:INT>>)
> STORED AS TEXTFILE;
> INSERT OVERWRITE TABLE text_tbl
> SELECT IF(false, named_struct("b", named_struct("c", 1)), NULL)
> FROM tbl LIMIT 1;
> CREATE TABLE parq_tbl
> STORED AS PARQUET
> AS SELECT * FROM text_tbl;
> SELECT * FROM text_tbl;
> => NULL # right
> SELECT * FROM parq_tbl;
> => {"b":{"c":null}} # wrong
> {code}
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