clickhouse-query
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.
Installation
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Usage
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skills listSkill Instructions
name: clickhouse-query description: 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.
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
--writableflag 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
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