在开发过程中，向hive分区表新增字段，发现查询新增字段的值为NULL

解决方法：对分区增加相应的字段
alter table student partition(pt = '2020-01-13') add columns(birthday string);

1.创建分区表，并插入数据

create table student(id int,name string) partitioned by (pt string);
insert into table student partition(pt = '2020-01-13') select 1,'lyn';
insert into table student partition(pt = '2019-01-14') select 2,'tom';

2. 查看数据

hive> select * from student;
OK
2   tom 2019-01-14
1   lyn 2020-01-13
Time taken: 0.189 seconds, Fetched: 2 row(s)

3. 增加字段

alter table student add columns(birthday string);
insert into table student partition(pt = '2020-01-13') select 1,'sarah','1990-01-01';
insert into table student partition(pt = '2020-01-14') select 2,'cici','1989-05-21';
insert into table student partition(pt = '2020-01-15') select 3,'land','1988-01-25';

4. 查看数据

hive> select * from student;
OK
2   tom NULL    2019-01-14
1   lyn NULL    2020-01-13
1   sarah   NULL    2020-01-13
2   cici    1989-05-21  2020-01-14
3   land    1988-01-25  2020-01-15
Time taken: 0.097 seconds, Fetched: 5 row(s)

5. 解决方法

-- 对于在增加字段前已经存在的分区，必须再执行
alter table student partition(pt = '2020-01-13') add columns(birthday string);

hive> select * from student;
OK
2   tom NULL    2019-01-14
1   lyn NULL    2020-01-13
1   sarah   1990-01-01  2020-01-13
2   cici    1989-05-21  2020-01-14
3   land    1988-01-25  2020-01-15
Time taken: 0.103 seconds, Fetched: 5 row(s)