Amazon Redshift will no longer support the creation of new Python UDFs starting Patch 198. Existing Python UDFs will continue to function until June 30, 2026. For more information, see the [ blog post ](https://aws.amazon.com/blogs/big-data/amazon-redshift-python-user-defined-functions-will-reach-end-of-support-after-june-30-2026/). 

# HLL\$1CREATE\$1SKETCH function
<a name="r_HLL_CREATE_SKETCH"></a>

The HLL\$1CREATE\$1SKETCH function returns an HLLSKETCH data type that encapsulates the input expression values. The HLL\$1CREATE\$1SKETCH 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
<a name="r_HLL_CREATE_SKETCH-synopsis"></a>

```
HLL_CREATE_SKETCH (aggregate_expression)
```

## Argument
<a name="r_HLL_CREATE_SKETCH-argument"></a>

 *aggregate\$1expression*   
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
<a name="r_HLL_CREATE_SKETCH-return-type"></a>

The HLL\$1CREATE\$1SKETCH function returns an HLLSKETCH value.

## Examples
<a name="r_HLL_CREATE_SKETCH-examples"></a>

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)
```