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)