Clickhouse sampling on MergeTree engine.
Why sampling is important and what you need to be aware of? When dealing with very large amount of data, you probably want to run your queries only for a smaller dataset in your current tables. Specially if your dataset is not fitting in RAM. MergeTree is the first and more advanced engine on Clickhouse that you want to try. It supports indexing by Primary Key and it is mandatory to have a column of Date type (used for automatic partitioning).