clickhouse-query

Apps & Automation

Run ClickHouse queries for analytics, metrics analysis, and event data exploration. Use when you need to query ClickHouse directly, analyze metrics, check event tracking data, or test query performance. Read-only by default.

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How to use this skill

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Source SKILL.md: https://github.com/civitai/civitai/blob/HEAD/.claude/skills/clickhouse-query/SKILL.md

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ClickHouse Query Testing

Use this skill to run ad-hoc ClickHouse queries for analytics, metrics analysis, and debugging.

Running Queries

Use the included query script:

node .claude/skills/clickhouse-query/query.mjs "SELECT count() FROM views"

Options

Flag	Description
`--explain`	Show query execution plan
`--writable`	Allow write operations (requires user permission)
`--timeout <s>`, `-t`	Query timeout in seconds (default: 30)
`--file`, `-f`	Read query from a file
`--json`	Output results as JSON
`--quiet`, `-q`	Minimal output, only results

Examples

# Count rows in a table
node .claude/skills/clickhouse-query/query.mjs "SELECT count() FROM views"

# Query with filters
node .claude/skills/clickhouse-query/query.mjs "SELECT * FROM modelEvents WHERE modelId = 123 LIMIT 10"

# Check query execution plan
node .claude/skills/clickhouse-query/query.mjs --explain "SELECT * FROM views WHERE userId = 1"

# Override default 30s timeout for longer queries
node .claude/skills/clickhouse-query/query.mjs --timeout 60 "SELECT ... (complex aggregation)"

# Query from file
node .claude/skills/clickhouse-query/query.mjs -f my-query.sql

# JSON output for processing
node .claude/skills/clickhouse-query/query.mjs --json "SELECT type, count() FROM modelEvents GROUP BY type"

Safety Features

Read-only by default: Blocks INSERT/ALTER/DROP unless --writable flag is used
30 second timeout: Prevents runaway queries (override with --timeout)
Explicit permission required: Before using --writable, you MUST ask the user for permission

When to Use --writable

Only use the --writable flag when:

The user explicitly requests write access
You need to insert test data
You're running maintenance operations

IMPORTANT: Always ask the user for permission before running with --writable.

Common Tables

Table	Description
`views`	Page/entity view events
`modelEvents`	Model create/publish/update events
`modelVersionEvents`	Model version events including downloads
`userActivities`	User registration, login, subscription events
`images`	Image upload/delete events
`reactions`	Like/dislike events
`reports`	Content report events
`entityMetricEvents`	Aggregated metric events

Querying Replica Clusters

IMPORTANT: Production uses a ClickHouse replica cluster. When querying system tables (logs, metrics, etc.), you must use clusterAllReplicas() to get data from all nodes.

System Tables on Replica Clusters

-- WRONG: Only queries the node you're connected to
SELECT * FROM system.query_log WHERE event_time > now() - INTERVAL 1 HOUR

-- CORRECT: Queries all replicas in the cluster
SELECT * FROM clusterAllReplicas(default, system.query_log)
WHERE event_time > now() - INTERVAL 1 HOUR

Common System Table Queries

-- Find recent queries across all nodes
SELECT
    hostname(),
    event_time,
    query_duration_ms,
    formatReadableSize(memory_usage) AS memory,
    query
FROM clusterAllReplicas(default, system.query_log)
WHERE type = 'QueryFinish'
    AND event_time > now() - INTERVAL 5 MINUTE
ORDER BY event_time DESC
LIMIT 20

-- Find expensive queries by memory usage (last 24 hours)
SELECT
    count() as query_count,
    user,
    sum(memory_usage) AS total_memory,
    normalized_query_hash
FROM clusterAllReplicas(default, system.query_log)
WHERE event_time > now() - INTERVAL 1 DAY
    AND query_kind = 'Select'
    AND type = 'QueryFinish'
GROUP BY normalized_query_hash, user
ORDER BY total_memory DESC
LIMIT 10

-- Search query logs by pattern
SELECT event_time, query_id, query, type
FROM clusterAllReplicas(default, merge('system', '^query_log*'))
WHERE query ILIKE '%some_table%'
    AND event_time > now() - INTERVAL 5 MINUTE

-- Debug a specific query across all nodes
SELECT hostname(), message
FROM clusterAllReplicas(default, system.text_log)
WHERE query_id = 'your-query-id-here'
ORDER BY event_time_microseconds ASC

When to Use clusterAllReplicas()

Use Case	Function
System tables (query_log, text_log, etc.)	`clusterAllReplicas(default, system.table_name)`
Application tables (views, modelEvents, etc.)	Direct query (already distributed)
Search multiple system tables	`clusterAllReplicas(default, merge('system', '^pattern*'))`

ClickHouse SQL Tips

-- Use count() not COUNT(*)
SELECT count() FROM views

-- Date filtering with toDate()
SELECT * FROM views WHERE toDate(time) = today()

-- Last 7 days
SELECT * FROM modelEvents WHERE time > now() - INTERVAL 7 DAY

-- Aggregations
SELECT type, count() as cnt FROM modelEvents GROUP BY type ORDER BY cnt DESC