add jar datasketches-memory-2.0.0.jar;
add jar datasketches-java-3.1.0.jar;
add jar datasketches-hive-1.2.0.jar;

create temporary function data2sketch as 'org.apache.datasketches.hive.hll.DataToSketchUDAF';
create temporary function unionSketches as 'org.apache.datasketches.hive.hll.UnionSketchUDAF';
create temporary function estimate as 'org.apache.datasketches.hive.hll.SketchToEstimateUDF';

use <your-db-name-here>;

-- prepare input data
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');

-- build sketches per category
create temporary table sketch_intermediate (category char(1), sketch binary);
insert into sketch_intermediate select category, data2sketch(id) from sketch_input group by category;

-- get unique count estimates per category
select category, estimate(sketch) from sketch_intermediate;

Output:
a	10.000000223517425
b	10.000000223517425

-- union sketches across categories and get overall unique count estimate
select estimate(unionSketches(sketch)) from sketch_intermediate;

Output:
15.000000521540663

add jar datasketches-memory-2.0.0.jar;
add jar datasketches-java-3.1.0.jar;
add jar datasketches-hive-1.2.0.jar;

create temporary function data2sketch as 'org.apache.datasketches.hive.hll.DataToSketchUDAF';
create temporary function estimate as 'org.apache.datasketches.hive.hll.SketchToEstimateUDF';
create temporary function unionTwoSketches as 'org.apache.datasketches.hive.hll.UnionSketchUDF';

use <your-db-name-here>;

-- prepare input data
create temporary table sketch_input (id1 int, id2 int);
insert into table sketch_input values (1, 2), (2, 4), (3, 6), (4, 8), (5, 10), (6, 12), (7, 14), (8, 16), (9, 18), (10, 20);

-- build two sketches
create temporary table sketch_intermediate (sketch1 binary, sketch2 binary);
insert into sketch_intermediate select data2sketch(id1), data2sketch(id2) from sketch_input;

-- get estimates from sketches and union
select estimate(sketch1), estimate(sketch2), estimate(unionTwoSketches(sketch1, sketch2)) from sketch_intermediate;

Output:
10.000000223517425	10.000000223517425	15.000000521540663