It seems that all Hive columns (at least those of primitive types) are always NULLable? What about columns of type STRUCT?
The following: echo 1,2 >twovalues.csv hive CREATE TABLE tc (x INT, y INT) ROW FORMAT DELIMITED FIELDS TERMINATED BY ','; LOAD DATA LOCAL INPATH 'twovalues.csv' INTO TABLE tc; CREATE TABLE oc (z STRUCT<a: int, b: int>); INSERT INTO TABLE oc SELECT null FROM tc; produces the error FAILED: SemanticException [Error 10044]: Line 1:18 Cannot insert into target table because column number/types are different 'oc': Cannot convert column 0 from void to struct<a:int,b:int>. I initially discovered such behavior with Avro-backed tables, and even entered a JIRA https://issues.apache.org/jira/browse/HIVE-4022 but now I realized it happens with CSV-backed tables as well. Perhaps related, perhaps not, it seems that all members of a STRUCT are always non-NULLable. The following: INSERT INTO TABLE oc SELECT named_struct('a', null, 'b', null) FROM tc; produces the error: FAILED: SemanticException [Error 10044]: Line 1:18 Cannot insert into target table because column number/types are different 'oc': Cannot convert column 0 from struct<a:void,b:void> to struct<a:int,b:int>.
