Querydown

Querydown is a modern domain-specific programming language for expressively writing relational databases queries that compile to SQL. The code is succinct and safe for end-users to write, making it like "markdown for SQL". The Querydown compiler is written in Rust.

Use case

Developers write HTML — users write Markdown.

Developers write SQL — users write... Querydown!

Querydown is intended to be a general-purpose, schema agnostic library that applications can incorporate to give their users powerful searching and reporting capabilities. While other compile-to-SQL languages like PRQL and Malloy are designed for developers and data scientists, Querydown is designed for less-technical users — the sort of people who are comfortable writing a formula in a spreadsheet but squeamish with SQL. Writing common sorts of queries in Querydown is much easier than writing them in SQL. However, Querydown can't express everything that SQL can (just like Markdown can't express everything that HTML can).

Status

⚠️ Querydown is currently in very early development. ⚠️

• The language design is still in flux, but only changing slowly.
• Parsing is implemented for most of the language, as currently designed.
• Compilation is implemented for some simple queries, but there is still a lot of work to do here!
• PostgreSQL is the only dialect implemented so far.

Example

Given an example issue-tracker schema...

• Find issues
• that were created in the past 6 months,
• and have no assignments,
• and have at least one label which is named "regression" or named "bug",
• and have between 10 and 20 comments by users whose team is not named "backend".
• Show all columns in the issues table.
• Show the author's username,
• Show the date of the first comment by anyone — while also sorting the results on that date (with the most recent values shown first).

(The bullet points above correspond, line for line, with the querydown code below)

#issues
created_at:>@6M|ago
--#assignments
++#labels{name:..["Regression" "Bug"]}
10..20:#comments{user.team.name!"Backend"}
$*
$author.username
$#comments.created_at%min \sd

Documentation

Documentation

Design goals

• Expressive and succinct
• Safety from arbitrary joins which may cause unwanted compute if missing the proper ON clause
• No keywords
• All queries begin with one base table
• Results never have more rows than are present in the base table

How it works

The querydown processor does the following

1. Takes input
   • Querydown code
   • Database schema (so that it knows about foreign keys)
   • (optionally) Additional schema hints (like pseudo foreign keys)
   • (optionally) Other global settings
2. Produces output
   • SQL
   • Information about the origin of each column in the results (so that cells may be updated)

Intentional limitations

• It only produces SELECT queries.
• Requires knowledge of schema
• Joinable tables are specified by configuration. You can't join arbitrary tables.