HLL_ COMBINE _ SKETCHES fungsi

HLL_ COMBINE _ SKETCHES adalah fungsi skalar yang mengambil dua HLLSKETCH nilai input dan menggabungkannya menjadi satuHLLSKETCH.

Kombinasi dua atau lebih HyperLogLog sketsa adalah sketsa baru HLLSKETCH 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 HLLSKETCH tipe, seperti nama kolom.

Jenis pengembalian

SKETCHESFungsi HLL COMBINE _ _ mengembalikan HLLSKETCH tipe.

Contoh

Contoh berikut mengembalikan HLLSKETCH nilai-nilai gabungan dalam tabelhll_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;