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Hive, mail # user - How are nulls represented in data?

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How are nulls represented in data?
Pradeep Kamath 2010-08-09, 16:42
   What value does hive expect in the data for a column to be treated as null? I tried some permutations on a text data based table but couldn't figure out what the correct representation was. I tried empty string, the string NULL and the string null for a string column and in all three cases the "is null" operator returned false.

A couple of related questions:
 - Does the representation of null depend on the type of the column - is it different for string Vs non-string columns?
 - Is the representation of null different for different storage formats - text Vs RCFile Vs SequenceFile - I am particularly interested in text and RCFile.

Thanks in advance,

Ning Zhang 2010-08-09, 18:46
yongqiang he 2010-08-09, 20:07