hive - 在 Hive 中将空白转换为 NULL

Question

我试图通过设置属性 'serialization.null.format' = '' 将源文件中的空白值转换为配置单元表中的 NULL。我在配置单元中编写的查询是:

create table test(a int, b string) stored as parquet TBLPROPERTIES('serialization.null.format'='');

然后通过 impala 向其中插入值，如下所示:

insert overwrite table test values (1, ''), (2, 'b');

结果显示如下:

| a | b |


| 1 |   |

| 2 | b |

有人可以帮我解决为什么空白没有转换为 NULL 吗？

Answer 1

问题是 Parquet SerDe。查看问题 https://issues.apache.org/jira/browse/HIVE-12362 .

说明如下:

create table src (a string);
insert into table src values (NULL), (''), ('');

0: jdbc:hive2://localhost:10000/default> select * from src;
+-----------+--+
| src.a  |
+-----------+--+
| NULL      |
|                |
|                |
+-----------+--+

create table dest (a string) row format serde 'org.apache.hadoop.hive.ql.io.parquet.serde.ParquetHiveSerDe' stored as INPUTFORMAT 'org.apache.hadoop.hive.ql.io.parquet.MapredParquetInputFormat' OUTPUTFORMAT 'org.apache.hadoop.hive.ql.io.parquet.MapredParquetOutputFormat';

alter table dest set SERDEPROPERTIES ('serialization.null.format' = '');
alter table dest set TBLPROPERTIES ('serialization.null.format' = '');
insert overwrite table dest select * from src;

0: jdbc:hive2://localhost:10000/default> select * from test11;
+-----------+--+
| test11.a  |
+-----------+--+
| NULL      |
|                |
|                |
+-----------+--+