# DuckDB 1.5.6: lesson test 2026-10-11 (passed)

Cite: headlesson test:thklu3q — DuckDB 1.5.6, 2026-10-11: 6/6 lesson steps passed (operator record). On 2026-10-11, the headlesson operator ran all 6 steps of this lesson with DuckDB 1.5.6 (macOS26.5.2 arm64; Homebrew duckdb 1.5.6 bottle installed during this test; self-made CSV input only), and all passed. The final Next step is advice and was not run. An independent check (revision 3fadc9d) covered: The installation step was not performed during the independent check, so 0 of 6 steps were verified consecutively from the start of the lesson. The outputs of the later five steps were checked separately, and values matched across JSON, CSV and Parquet. Its limits: Not an independent pass of the whole lesson. The JSON sum is a string and the Parquet type is DOUBLE. This is the operator's own run, not a vendor claim. https://headlesson.com/tests/thklu3q

Record test:thklu3q. Question: Create a small CSV, aggregate it with SQL and get the result as JSON and CSV.

## Answer

On 2026-10-11, the headlesson operator ran all 6 steps of this lesson with DuckDB 1.5.6 (macOS26.5.2 arm64; Homebrew duckdb 1.5.6 bottle installed during this test; self-made CSV input only), and all passed. The final Next step is advice and was not run. An independent check (revision 3fadc9d) covered: The installation step was not performed during the independent check, so 0 of 6 steps were verified consecutively from the start of the lesson. The outputs of the later five steps were checked separately, and values matched across JSON, CSV and Parquet. Its limits: Not an independent pass of the whole lesson. The JSON sum is a string and the Parquet type is DOUBLE. This is the operator's own run, not a vendor claim.

## Tested on

- Test date: 2026-10-11
- Record confirmed: 2026-10-11
- Version: 1.5.6
- Environment: macOS26.5.2 arm64; Homebrew duckdb 1.5.6 bottle installed during this test; self-made CSV input only
- Result: passed, 6/6 steps

## Lesson steps and what happened

- 1. [passed] brew install duckdb
- 2. [passed] duckdb --version
- 3. [passed] printf 'region,product,amount\nnorth,apple,3\nnorth,pear,5\nsouth,apple,7\nsouth,apple,1\neast,pear,4\n' > sales.csv
- 4. [passed] duckdb -init /dev/null -json -c "SELECT region, count(*) AS n, sum(amount) AS total FROM 'sales.csv' GROUP BY region ORDER BY total DESC"
- 5. [passed] duckdb -init /dev/null -csv -c "SELECT product, avg(amount) AS avg_amount FROM read_csv('sales.csv') GROUP BY product ORDER BY product"
- 6. [passed] duckdb -init /dev/null -c "COPY (SELECT region, sum(amount) AS total FROM 'sales.csv' GROUP BY region) TO 'totals.parquet' (FORMAT parquet)"

## Next (advice, not tested)

Next: Agree with the user on the real data files and whether any output file may be written; run DESCRIBE SELECT * FROM '<file>' first to check the inferred column types, then run the aggregate with -json and compare row counts with the source.

## Cautions recorded with the lesson

These notes come from the lesson. Some describe failures seen in tests; others are general cautions. Each one is not a separately tested result.

- sum() over an integer column returns HUGEINT, which -json prints as a quoted string (for example "total":"8"); CAST to BIGINT or DOUBLE when a JSON number is needed.
- The CLI runs ~/.duckdbrc on startup; pass -init /dev/null for a reproducible run.
- Column types are inferred from the CSV contents; check them with DESCRIBE before relying on numeric or date columns.
- Without a database file the CLI uses a temporary in-memory database; tables created there are lost when the command exits.
- Rows with equal ORDER BY values come back in no guaranteed order; add a tie-breaker column for stable output.
- Confirm: Check which files a query reads and writes (COPY ... TO overwrites paths) and confirm row counts and types before passing results to a downstream step.

## What this record does not show

- Not measured in this run: remote files (httpfs/S3).
- Not measured in this run: extension installation over the network.
- Not measured in this run: large files.
- Not measured in this run: the web UI.
- Not measured in this run: safe mode.
- Not measured in this run: real user data.
- Whether an agent new to this tool can use it from this record alone (the operator wrote and ran the lesson).
- Comparisons between models or clients.
- Production use, accounts, or real customer data.
- Behaviour of the latest version (the test is tied to the version and date below).
- The final "Next" step is advice and was not part of the test.

## Primary record

Operator record: a past lesson trial (legacy). It is not claimed to meet level L1 of run-task-contract/0.1.0.

## Independent check

Independent check (revision 3fadc9d6215b): The installation step was not performed during the independent check, so 0 of 6 steps were verified consecutively from the start of the lesson. The outputs of the later five steps were checked separately, and values matched across JSON, CSV and Parquet.

Limits: Not an independent pass of the whole lesson. The JSON sum is a string and the Parquet type is DOUBLE.

## Evidence

A non-public test report exists and is not published, so third parties cannot check it directly.

## Retrieve over MCP

`headlesson_get id="app:duckdb" sections ["lesson","gotchas"]` on https://mcp.headlesson.com/mcp

## Source version

This page is built from the catalog record app:duckdb at revision 9bafd789f564. It is not rewritten when the current lesson changes; a new test gets a new record ID.

## Sources (lesson text at the fixed revision)

Each line names fields of this page (as JSON pointers into the .json version) and where they come from. Labels without a link are non-public sources. Fields not listed (such as test results) are the headlesson operator's own observations.

- /question, /next_advice, /cautions/items/2, /cautions/items/4, /cautions/items/5: headlesson editorial judgement (checked 2026-10-11, inferred, editorial)
- /steps/0/step: [https://duckdb.org/install/](https://duckdb.org/install/) (checked 2026-10-11, primary, official)
- /steps/1/step, /steps/2/step, /steps/3/step, /steps/4/step, /steps/5/step, /cautions/items/0: headlesson editorial judgement (checked 2026-10-11, primary, editorial)
- /cautions/items/1, /cautions/items/3: [https://duckdb.org/docs/current/clients/cli/overview.html](https://duckdb.org/docs/current/clients/cli/overview.html) (checked 2026-10-11, primary, official)

## Corrections

None.

Page updated: 2026-10-13 (the date its content last changed).

要約（日本語）: DuckDB の lesson を 2026-10-11 に headlesson の運営が 1.5.6 で試し、6/6 段が通った（passed、運営の実測で製品側の主張ではない）。この記録が示さないこと・独立確認の状況は本文のとおり。