chdb-sql

Runs SQL queries over files on your disk, over cloud storage and over other databases, all from inside a Python script and with no database server to install or keep running.

WHEN TO USE

SCOPE

USE FOR

Run a one-off analytical SQL query over a local parquet or CSV file.
Join a MySQL database table with a parquet file stored in Amazon S3, all in one SQL statement.
Create tables once and keep querying them across several steps of an analysis.
Plug chdb into code that expects a standard Python database connection and cursor.

NOT FOR

Chain pandas-style DataFrame methods; use the chdb-datastore skill instead.

This is a saved copy of the skill's SKILL.md instructions. It may differ from the upstream file or the version you install.

In this document (7)

chdb SQL — ClickHouse in Your Python Process

Run ClickHouse SQL directly in Python — no server needed. Query local files, remote databases, and cloud storage with full ClickHouse SQL power.

pip install chdb

Decision Tree: Pick the Right API

1. One-off query on files or databases → chdb.query()
2. Multi-step analysis with tables      → Session
3. DB-API 2.0 connection                → chdb.connect()
4. Pandas-style DataFrame operations    → Use chdb-datastore skill instead

chdb.query() — One Line, Any Data

import chdb

chdb.query("SELECT * FROM file('data.parquet', Parquet) WHERE price > 100 LIMIT 10")       # local files
chdb.query("SELECT * FROM mysql('db:3306', 'shop', 'orders', 'root', 'pass')")              # databases
chdb.query("SELECT * FROM s3('s3://bucket/data.parquet', NOSIGN) LIMIT 10")                 # cloud storage
chdb.query("SELECT * FROM deltaLake('s3://bucket/delta/table', NOSIGN) LIMIT 10")           # data lakes

# Cross-source join
chdb.query("""
    SELECT u.name, o.amount FROM mysql('db:3306', 'crm', 'users', 'root', 'pass') AS u
    JOIN file('orders.parquet', Parquet) AS o ON u.id = o.user_id ORDER BY o.amount DESC
""")

data = {"name": ["Alice", "Bob"], "score": [95, 87]}
chdb.query("SELECT * FROM Python(data) ORDER BY score DESC")                                # Python data
df = chdb.query("SELECT * FROM numbers(10)", "DataFrame")                                   # output formats
chdb.query("SELECT toDate({d:String}) + number FROM numbers({n:UInt64})",
    "DataFrame", params={"d": "2025-01-01", "n": 30})                                      # parametrized

Table functions → table-functions.md | SQL functions → sql-functions.md | Full API → api-reference.md

Session — Stateful Analysis Pipelines

from chdb import session as chs
sess = chs.Session("./analytics_db")   # persistent; Session() for in-memory

sess.query("CREATE TABLE users ENGINE=MergeTree() ORDER BY id AS SELECT * FROM mysql('db:3306','crm','users','root','pass')")
sess.query("CREATE TABLE events ENGINE=MergeTree() ORDER BY (ts,user_id) AS SELECT * FROM s3('s3://logs/events/*.parquet',NOSIGN)")
sess.query("""
    SELECT u.country, count() AS cnt, uniqExact(e.user_id) AS users
    FROM events e JOIN users u ON e.user_id = u.id
    WHERE e.ts >= today() - 7 GROUP BY u.country ORDER BY cnt DESC
""", "Pretty").show()
sess.close()

Connection API (DB-API 2.0)

from chdb import dbapi
conn = dbapi.connect()
cur = conn.cursor()
cur.execute("SELECT * FROM file('data.parquet', Parquet) WHERE value > 100")
print(cur.fetchall())
cur.close()
conn.close()

Troubleshooting

Problem	Fix
`ImportError: No module named 'chdb'`	`pip install chdb`
`DB::Exception: FILE_NOT_FOUND`	Check file path; use absolute path or verify cwd
`DB::Exception: Unknown table function`	Check function name spelling (e.g., `deltaLake` not `deltalake`)
Connection refused to remote DB	Check host:port format; ensure remote DB allows connections
Environment check	Run `python scripts/verify_install.py` (from skill directory)

References

API Reference — query/Session/connect signatures
Table Functions — All ClickHouse table functions
SQL Functions — Commonly used SQL functions
Examples — 9 runnable examples with expected output
Official Docs

Note: This skill teaches how to use chdb SQL. For pandas-style operations, use the chdb-datastore skill. For contributing to chdb source code, see CLAUDE.md in the project root.

This skill ships inside the ClickHouse Agent Skills plugin.

Run this outside your AI tool, using Node.js 22.20.0 or newer. Skills CLI 1.7.2 skips skill selection; prompts cancel installation without an interactive terminal. If choosing Project when asked about installation scope, open your project's folder before running this.

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npx skills add clickhouse/agent-skills --skill "chdb-sql" --full-depth

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What's inside

Files included with this skill.

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