ClickHouse Conquers Advent of Code: SQL's Triumph

ClickHouse: SQL's Advent Victory

The key insight of this article is the demonstration of ClickHouse's versatility, showing its capability to tackle complex algorithmic problems typically solved with general-purpose programming languages. The use of pure SQL, avoiding UDFs and temporary tables, is particularly noteworthy, showcasing the power of ClickHouse's vectorized query engine and analytical functions. The article's innovation lies in challenging the conventional wisdom that SQL is unsuitable for problems requiring state management and complex data structures. The detailed implementation, especially the use of arrayJoin and arrayFold functions, provides valuable insights for developers seeking to optimize their SQL queries and explore ClickHouse's advanced features.

However, the article's limitations include its narrow focus on Advent of Code challenges, which, while impressive, don't necessarily reflect real-world business use cases. The complex SQL queries, while demonstrating ClickHouse's power, can also be difficult to read, debug, and maintain compared to solutions in languages like Python. Furthermore, the article doesn't provide a comparative analysis with other databases or SQL dialects, limiting the context of the achievement. The target audience is primarily ClickHouse users and SQL enthusiasts interested in optimization and pushing the boundaries of what's possible with SQL. A more in-depth discussion of performance trade-offs, particularly in comparison to UDF-based approaches or external tools, would have enhanced the analysis.

Technically, the use of window functions, array functions, and CTEs is crucial. The reliance on these features underscores the engine's capabilities. The implication is that ClickHouse can be used for more than just OLAP, potentially extending its reach into areas where real-time stream processing and complex data manipulation are required. The performance impact of such complex queries in a production environment needs further investigation. A comparison against solutions using procedural languages or other databases like PostgreSQL (with its extensive extensions) would have been beneficial for understanding the relative advantages and disadvantages of the ClickHouse approach.

Key Points

• ClickHouse was used to solve Advent of Code challenges using pure SQL, demonstrating its versatility beyond OLAP.

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📖 Source: Solving the "Impossible" in ClickHouse: Advent of Code 2025