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ClickHouse

Test data in ClickHouse.

1. Install​

uv tool install --python python3.11 --upgrade 'datacontract-cli[clickhouse]'

See Installation for pip, pipx, and Docker.

2. Authenticate​

Create a .env file in your working directory (or export the variables):

# .env
DATACONTRACT_CLICKHOUSE_USERNAME=analyst
DATACONTRACT_CLICKHOUSE_PASSWORD=mysecretpassword

Without them, the CLI connects as ClickHouse's default user with an empty password. For ClickHouse Cloud, set DATACONTRACT_CLICKHOUSE_SECURE=true — see the ClickHouse Reference.

3. Create a contract from your tables​

Import the table metadata directly from system.columns. This also generates a ready-to-test servers block:

datacontract import clickhouse \
  --source localhost \
  --database sales \
  --table orders \
  --output datacontract.yaml

Repeat --table for multiple tables, or omit it to import every table and view in the database. Add --port if the HTTP interface doesn't listen on the default 8123.

Only have a DDL script? datacontract import sql --source orders.sql --dialect clickhouse works too, but writes a servers block with placeholder values that you have to fill in by hand.

4. Test the actual data​

datacontract test datacontract.yaml
Testing datacontract.yaml
Server: clickhouse (type=clickhouse, host=localhost, port=8123, database=sales)
╭────────┬──────────────────────────────────────────────────────────┬──────────┬─────────╮
│ Result │ Check                                                    │ Field    │ Details │
├────────┼──────────────────────────────────────────────────────────┼──────────┼─────────┤
│  ...   │                                                          │          │         │
│ passed │ Check that field 'order_id' is present                   │ order_id │         │
│ passed │ Check that field order_id has physical type String       │ order_id │         │
│ passed │ Check that field order_id has no missing values          │ order_id │         │
│  ...   │                                                          │          │         │
╰────────┴──────────────────────────────────────────────────────────┴──────────┴─────────╯
🟢 Data contract is valid. Run 33 checks. Took 0.5 seconds.

5. Let it catch a violation​

The contract becomes valuable when it detects drift. Tighten an expectation — for example, add a quality rule to a schema in datacontract.yaml:

schema:
  - name: orders
    # ...
    quality:
      - type: sql
        description: No order has a negative total
        query: SELECT countIf(order_total < 0) FROM orders
        mustBe: 0

Run datacontract test datacontract.yaml again: every violation is listed as an error, and the command exits with code 1 — ready for CI/CD and scheduled runs so you catch drift before your consumers do.

Reference​

All authentication options and the data type handling: ClickHouse Reference.

Troubleshooting​

  • Port 9000 is for clickhouse-client program — the CLI talks to ClickHouse over HTTP. A contract that names the native port 9000 (or 9440) is connected to 8123 (or 8443) automatically; any other native port has to be replaced by the HTTP port in the servers block or with DATACONTRACT_CLICKHOUSE_PORT.
  • Authentication failed — set DATACONTRACT_CLICKHOUSE_USERNAME and DATACONTRACT_CLICKHOUSE_PASSWORD; without them the CLI logs in as default.