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


HLL_CARDINALITY (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.


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)