HLL_ CARDINALITY fungsi

CARDINALITYFungsi HLL _ mengembalikan kardinalitas tipe HLLSKETCH data input.

Sintaks

HLL_CARDINALITY (hllsketch_expression)

Pendapat

hllsketch_expression

Ekspresi valid apa pun yang mengevaluasi HLLSKETCH tipe, seperti nama kolom. Nilai input adalah tipe HLLSKETCH data.

Jenis pengembalian

CARDINALITYFungsi HLL _ mengembalikan INT8 nilai BIGINT atau.

Contoh

Contoh berikut mengembalikan kardinalitas kolom sketch dalam tabel. hll_table

CREATE TABLE a_table(an_int INT, b_int INT);
INSERT INTO a_table VALUES (1,1), (2,1), (3,1), (4,1), (1,2), (2,2), (3,2), (4,2), (5,2), (6,2);

CREATE TABLE hll_table (sketch HLLSKETCH);
INSERT INTO hll_table select hll_create_sketch(an_int) from a_table group by b_int;

SELECT hll_cardinality(sketch) AS cardinality FROM hll_table;
cardinality
-------------
6
4
(2 rows)