Hive textfile 格式 Null 和 ‘‘ 的处理

create table t1(c1 string, c2 string) row format delimited fields terminated by ',' stored as textfile;

vim t1.txt

N,1
,2

load data local inpath 't1.txt' overwrite into table t1;

hive> select * from t1;
OK
NULL	1
	    2
Time taken: 0.924 seconds, Fetched: 2 row(s)
hive> select * from t1 where c1 is null;
OK
NULL	1
Time taken: 0.293 seconds, Fetched: 1 row(s)
hive> select * from t1 where c1 = '';
OK
	2
Time taken: 0.108 seconds, Fetched: 1 row(s)

如果已经有数据，需要把长度为 0 的字符串认为 NULL。
t2.txt 文件 。

1,,2
3,4,5

t2.txt 文件第 1 行, 之间没有任何字符，默认 hive 不会把此列认为是 NULL

create table t2(c1 string, c2 string,c3 string) row format delimited fields terminated by ',' stored as textfile;

load data local inpath 't2.txt' overwrite into table t2;

hive>  select * from t2 where c2 is null;
OK
Time taken: 1.184 seconds
hive> select * from t2 where c2 = '';
OK
1		2
Time taken: 0.106 seconds, Fetched: 1 row(s)
hive> 

如果需要默认为 NULL，设置 serdeproperties 属性。

 alter table t2 set serdeproperties('serialization.null.format' = '');
hive> select * from t2 where c2 is null;
OK
1	NULL	2
Time taken: 0.149 seconds, Fetched: 1 row(s)
hive> select * from t2 where c2 = '';
OK
Time taken: 0.148 seconds