HLL_CREATE_SKETCH function
The HLL_CREATE_SKETCH function returns an HLLSKETCH data type that encapsulates the
input expression values. The HLL_CREATE_SKETCH function works with any data type and
ignores NULL values. When there are no rows in a table or all rows are NULL, the
resulting sketch has no index-value pairs such as
{"version":1,"logm":15,"sparse":{"indices":[],"values":[]}}.
Syntax
HLL_CREATE_SKETCH (aggregate_expression)
Argument
- aggregate_expression
-
Any valid expression that provides the value to an aggregate, such as a column name. NULL values are ignored. This function supports any data type as input except HLLSKETCH, GEOMETRY, GEOGRAPHY, and VARBYTE.
Return type
The HLL_CREATE_SKETCH function returns an HLLSKETCH value.
Examples
The following example returns the HLLSKETCH type for column an_int in
table a_table. A JSON object is used to represent a sparse HyperLogLog
sketch when importing, exporting, or printing sketches. A string representation (in
Base64 format) is used to represent a dense HyperLogLog sketch.
CREATE TABLE a_table(an_int INT); INSERT INTO a_table VALUES (1), (2), (3), (4); SELECT hll_create_sketch(an_int) AS sketch FROM a_table; sketch ------------------------------------------------------------------------------------------------------- {"version":1,"logm":15,"sparse":{"indices":[20812342,20850007,22362299,47158030],"values":[1,2,1,1]}} (1 row)