hive sql find the latest record

Question

the table is:

create table test (
id string,
name string,
age string,
modified string)

data like this:

id    name   age  modife         


        

Answer 1

Presume the data is like this:

    id      name    age     modifed
    1       a       10      2011-11-11 11:11:11
    1       a       11      2012-11-11 12:00:00
    2       b       23      2012-12-10 10:11:12
    2       b       21      2012-12-10 10:11:12
    2       b       22      2012-12-15 10:11:12
    2       b       20      2012-12-15 10:11:12

then the result of the above query will give you - (notice the repeated 2, b having the same date time)

    1       a       11      2012-11-11 12:00:00
    2       b       22      2012-12-15 10:11:12
    2       b       20      2012-12-15 10:11:12

This query runs an additional group by and is less efficient but gives the correct result -

    select collect_set(b.id)[0], collect_set(b.name)[0], collect_set(b.age)[0], b.modified
    from
        (select id, max(modified) as modified from test group by id) a
      left outer join
        test b
      on
        (a.id=b.id and a.modified=b.modified)
    group by
      b.modified;

then the result of the above query will give you

    1       a       11      2012-11-11 12:00:00
    2       b       20      2012-12-15 10:11:12

Now if we improve the query a little - then in place of 3 MRs it runs only one Keping the result same -

    select id, collect_set(name)[0], collect_set(age)[0], max(modified)
    from test 
    group by id;

Note - this will slow down in case your group by field produces large results.

Answer 2

You can get the required result without using left outer join like this:

select * from test where (id, modified) in(select id, max(modified) from test group by id)

http://sqlfiddle.com/#!2/bfbd5/42