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@d284161 official
by clickhouseclickhouse/agent-skills543 stars
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MUST USE when reviewing ClickHouse schemas, queries, or configurations. Contains 31 rules that MUST be checked before providing recommendations. Always read relevant rule files and cite specific rules in responses.

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Use this Skill: https://skilld.dev/gh/clickhouse/agent-skills/clickhouse-best-practices

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rulesquery-join-null-handling.md

≈267 tokens on demand. Your agent reads this file only when SKILL.md points to it.

Optimize NULL Handling in Outer JOINs

Impact: MEDIUM

Set join_use_nulls = 0 to use default column values instead of NULL markers, reducing memory overhead compared to Nullable wrappers.

Example:

-- Use default values instead of NULLs for non-matching rows
SET join_use_nulls = 0;

SELECT o.order_id, c.name
FROM orders o
LEFT JOIN customers c ON c.id = o.customer_id;
-- Non-matching rows get '' for name instead of NULL

When to use:

Setting Behavior Use Case
join_use_nulls = 0 (default) Default values (empty string, 0) for non-matches When you can handle default values
join_use_nulls = 1 NULL for non-matches When you need to distinguish "no match" from "matched with default"

Reference: Minimize and Optimize JOINs

Source: SKILL.md on GitHub

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  • Gen Agent Trust Hub17d

    This skill provides comprehensive best practices for ClickHouse database management, including schema design, query optimization, and ingestion strategies. It includes robust safety guardrails for AI agents, such as mandatory query limits, execution timeouts, and a structured schema discovery workflow. All external references and tools trace back to official ClickHouse vendor resources.

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Provenance

Signed by skilld at d284161. This ties the file your Agent reads to that commit on GitHub. It does not review the instructions.

Last checked against GitHub 3 days ago.

Activeupdated 5 months ago

Capability

metadata
{
  "author": "ClickHouse Inc",
  "version": "0.4.0"
}

Topics

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What it does

Provides 31 ClickHouse-specific rules organized by priority across schema design, query optimization, data ingestion, and agent connectivity. Use this skill to validate schemas, review queries, and establish safe agent workflows with proper connection setup, schema discovery, and query safety procedures.

Generated from the current SKILL.md.

Frequently asked

When should I use this skill?
Use this skill when reviewing ClickHouse schemas, queries, or data ingestion strategies. It contains 31 rules covering primary key design, data types, JOINs, partitioning, and insert batching that you must check before providing ClickHouse recommendations.
Does this skill help with AI agent connectivity to ClickHouse?
Yes. The skill includes rules for MCP and CLI connection setup, schema discovery workflows, and query safety (LIMIT, timeouts, progressive exploration) specific to AI agents querying ClickHouse.
What should I do if a rule doesn't exist for my question?
Fall back to the LLM's ClickHouse knowledge, search the official ClickHouse documentation, or use web search. Always cite your source in the response.
Are the rules mandatory or advisory?
The rules are mandatory checks before answering ClickHouse questions. They encode ClickHouse-specific behaviors (columnar storage, merge tree mechanics, sparse indexes) where general database intuition can be misleading.
Can I use this skill for INSERT performance tuning?
Yes. The skill covers batch sizing (10K-100K rows), async inserts for high-frequency small batches, mutation avoidance (ReplacingMergeTree instead of ALTER UPDATE), and OPTIMIZE TABLE risks.

Generated from the current SKILL.md. These answers refresh after source changes.