Hive Left Semi Join for 'Not Exists'

Hive - Use NOT Exists in Using Semi Join

Solution:

Check the target tables have all the fields from both the tables. Because, here used *.

Then,
It should be b.VALUE IS NULL and not = NULL.

The query should be like this:

INSERT OVERWRITE TABLE A a 
SELECT * FROM B b 
LEFT SEMI JOIN C c 
ON (b.ID = c.ID AND b.VALUE = c.VALUE) where 
b.ID IS NULL AND b.VALUE IS NULL;

Using three or more joins within a single hive query

Yes, they are equivalent, although the results may not be in the same order in the result set. And if you used select *, then the columns would be in a different order.

The reason is a little subtle -- the outer joined table is not used anywhere else in the FROM clause. So, you don't have to worry about NULL values from non-matching rows.

As a general rule, I order joins in the FROM clause starting with inner joins and followed by outer joins. The clause becomes quite difficult to accurately follow when you start mixing join types. So, I recommend:

from a join
     b
     on a.key = b.key join
     c
     on a.key = c.key left join
     u
     on a.key = u.key

subquerying in hive with left outer join or where exists

After left outer join keep alias name for the all the query you have written to M then run the query again.

Try to run below Query:

select 
U.session_id,
U.session_date,
U.email
from data.usage U
left outer join
  (select 
  distinct M.session_id
  from data.usage M
  where email like '%gmail.com%'
  and data_date >= '20180101'
  and name in
    ( 
    select 
    lower(name)
    from data.users
    where role like 'Person%' 
    and isactive = TRUE
    and data_date = '20180412'
    ))M
on U.session_id = M.session_id

How to implement LEFT/RIGHT OUTER JOIN to replace NOT IN in hive query?

The query select S.* from empSrc S
where S.empid not in (select T.empid from empTrg T) doesn't actually perform a cross join. There is no problem with it.

The same logic can be replicated with not exists

select s.*
from empSrc s 
where not exists (select 1 from empTrg t where t.empid = s.empid)

or a left join.

select s.*
from empSrc s
left join empTrg t on t.empid = s.empid
where t.empid is null --condition to check for non existent records

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