HLL_CARDINALITY function

The HLL_CARDINALITY function returns the cardinality of the input HLLSKETCH data type.

Syntax

HLL_CARDINALITY (hllsketch_expression)

Argument

hllsketch_expression

Any valid expression that evaluates to an HLLSKETCH type, such as a column name. The input value is the HLLSKETCH data type.

Return type

The HLL_CARDINALITY function returns a BIGINT or INT8 value.

Examples

The following example returns the cardinality of column sketch in table 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)