Limitations - Amazon Redshift
Services or capabilities described in Amazon Web Services documentation might vary by Region. To see the differences applicable to the China Regions, see Getting Started with Amazon Web Services in China (PDF).


The following are limitations for using HyperLogLog in Amazon Redshift:

  • Amazon Redshift tables don't support an HLLSKETCH column as a sort key or a distribution key for an Amazon Redshift table.

  • Amazon Redshift doesn't support HLLSKETCH columns in ORDER BY, GROUP BY, or DISTINCT clauses.

  • You can only UNLOAD HLLSKETCH columns to text or CSV format. Amazon Redshift then writes the HLLSKETCH data in either a JSON format or a Base64 format. For more information about UNLOAD, see UNLOAD.

  • Amazon Redshift only supports HyperLogLog sketches with a precision (logm value) of 15.

  • JDBC and ODBC drivers don't support the HLLSKETCH data type. Therefore, the result set uses VARCHAR to represent the HLLSKETCH values.

  • Amazon Redshift Spectrum doesn't natively support the HLLSKETCH data. Therefore, you can't create or alter an external table with an HLLSKETCH column.

  • Data types for Python user-defined functions (UDFs) don't support the HLLSKETCH data type. For more information about Python UDFs, see Creating a scalar Python UDF.