Hive LEFT SEMI JOIN for 'NOT EXISTS'

Question

I have two tables with a single key column. Keys in table a are subset of all keys in table b. I need to select keys from table b that are NOT in table a.

Here is a

Answer 1

The answer to your issue should be

SELECT a.key FROM a LEFT OUTER JOIN b ON a.key = b.key WHERE b.key IS NULL;

This means, bring all the keys from a, irrespective of whether there is a match in b or not. The where cause will filter those records, which are not available in b.