How to choose a primary key in ClickHouse

Primary keys in ClickHouse serve a different purpose than traditional relational databases, as they are used for data organization and sparse indexing rather than enforcing uniqueness. Choosing the right primary key is crucial for optimizing data storage and query performance in ClickHouse. Factors to consider when selecting an optimal primary key include query patterns, column order, and data sorting. Practical tips include ordering low to high cardinality columns, picking filtering columns, organizing hierarchical data from root to leaves, and putting the timestamp as the latest column in the ORDER BY clause for time series data. By understanding ClickHouse's primary key functionality and following these guidelines, users can significantly enhance the performance and efficiency of their ClickHouse database.