[jira] [Created] (IMPALA-9633) Implement ds_hll_union() builtin function

["Gabor Kaszab (Jira)" <ji...@apache.org>]

Gabor Kaszab created IMPALA-9633:
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             Summary: Implement ds_hll_union() builtin function
                 Key: IMPALA-9633
                 URL: https://issues.apache.org/jira/browse/IMPALA-9633
             Project: IMPALA
          Issue Type: New Feature
          Components: Backend, Frontend
            Reporter: Gabor Kaszab


ds_hll_union() is an aggregating function that accepts sketches and produces a single scratch that is the combination of the received scratches.

Example from Hive:
{code:java}
create temporary table sketch_intermediate (category char(1), sketch binary);
insert into sketch_intermediate select category, ds_hll_sketch(id) from sketch_input group by category;
select ds_hll_estimate(ds_hll_union(sketch)) from sketch_intermediate;
{code}

Some test data for the example:
{code:java}
create temporary table sketch_input (id int, category char(1));
insert into table sketch_input values
  (1, 'a'), (2, 'a'), (3, 'a'), (4, 'a'), (5, 'a'), (6, 'a'), (7, 'a'), (8, 'a'), (9, 'a'), (10, 'a'),
  (6, 'b'), (7, 'b'), (8, 'b'), (9, 'b'), (10, 'b'), (11, 'b'), (12, 'b'), (13, 'b'), (14, 'b'), (15, 'b');
{code}

Approximate result:
{code:java}
15.000000521540663
{code}




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