Fungsi HLL_COMBINE_SKETCHES

PDFRSS

HLL_COMBINE_SKETCHES adalah fungsi skalar yang mengambil input dua nilai HLLSKETCH dan menggabungkannya menjadi satu HLLSKETCH.

Kombinasi dua atau lebih HyperLogLog sketsa adalah HLLSKETCH baru yang merangkum informasi tentang penyatuan nilai berbeda yang diwakili oleh setiap sketsa input.

Sintaks

HLL_COMBINE_SKETCHES (hllsketch_expression1, hllsketch_expression2)

Pendapat

hllsketch_expression1 dan hllsketch_expression2

Ekspresi valid apa pun yang mengevaluasi tipe HLLSKETCH, seperti nama kolom.

Jenis pengembalian

Fungsi HLL_COMBINE_SKETCHES mengembalikan tipe HLLSKETCH.

Contoh

Contoh berikut mengembalikan nilai HLLSKETCH gabungan dalam tabel. hll_table

WITH tbl1(x, y)
     AS (SELECT Hll_create_sketch(1),
                Hll_create_sketch(2)
         UNION ALL
         SELECT Hll_create_sketch(3),
                Hll_create_sketch(4)
         UNION ALL
         SELECT Hll_create_sketch(5),
                Hll_create_sketch(6)
         UNION ALL
         SELECT Hll_create_sketch(7),
                Hll_create_sketch(8)),
     tbl2(x, y)
     AS (SELECT Hll_create_sketch(9),
                Hll_create_sketch(10)
         UNION ALL
         SELECT Hll_create_sketch(11),
                Hll_create_sketch(12)
         UNION ALL
         SELECT Hll_create_sketch(13),
                Hll_create_sketch(14)
         UNION ALL
         SELECT Hll_create_sketch(15),
                Hll_create_sketch(16)
         UNION ALL
         SELECT Hll_create_sketch(NULL),
                Hll_create_sketch(NULL)),
     tbl3(x, y)
     AS (SELECT *
         FROM   tbl1
         UNION ALL
         SELECT *
         FROM   tbl2)
SELECT Hll_combine_sketches(x, y)
FROM   tbl3;