Is there any issues in keeping null values for rows (hbase)?

[#1]

Here i just need rowkey alone based on range based, Is there any problem in creating empty row alone throughout table.

Rowkey --> key1_date&time_key2

column --> empty

query --> select * from table where startkey=>key1_date&time and endkey=>key1_date&time

Goal is to extract key2

[#2]

You may want to take a step back and look at your access patterns. If this is the only way you are planning on accessing this data, you can move key2 into the value section since you are not searching on it. If you will sometimes be searching on key1+key2 then it makes sense to keep it as a key. You shouldn't have a problem with the value being null but usually in a key-value system there is some sort of value you are looking for, so be sure to understand what it is you're searching for in this scenario and structure your data properly.