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An interpreted relational query language that compiles to SQL

Project description

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Preql is an interpreted, relational programming language, that specializes in database queries.

It is designed for use by data engineers, analysts and data scientists.

Preql's main objective is to provide an alternative to SQL, in the form of a high-level programming language, with first-class functions, modules, strict typing, and Python integration.

How does it work?

Preql code is interpreted and gets compiled to SQL at runtime. This way, Preql gains the performance and abilities of SQL, but can also operate as a normal scripting language.

Currently supported dialects are:

  • Postgres
  • MySQL
  • Sqlite
  • BigQuery (WIP)
  • More... (planned)

For features that are database-specific, or aren't implemented in Preql, there is a SQL() function that provides a convenient escape hatch to write raw SQL code.

Main Features

  • Modern syntax and semantics
    • Interpreted, everything is an object
    • Strong type system with gradual type validation and duck-typing
  • Compiles to SQL
  • Python and Pandas integration
  • Interactive shell (REPL) with auto-completion
  • Runs on Jupyter Notebook

Note: Preql is still work in progress, and isn't ready for production use, or any serious use quite yet.


Learn More

Get started

Simply install via pip:

    pip install -U preql-lang

Then just run the interpreter:


Requires Python 3.6+

Read more

Quick Example

// Declare a new table
table Continent {
    name: string
    area: int       // km²
    population: int

// Initialize the table, by inserting rows
new Continent("Africa", 30370000, 1287920000)
new Continent("Antarctica", 14000000, 4490)
new Continent("Asia", 44579000, 4545133000)
new Continent("Europe", 10180000, 742648000)
new Continent("North America", 24709000, 587615000)
new Continent("South America", 17840000, 428240000)
new Continent("Australia", 8600000, 41261000)

// Print the continents, ordered by density
print Continent {
    ...                         // Include existing fields
    density: population / area  // Create new a field

} order{^density}

// Print the total land area
print "Total land area:", sum(Continent{area}), "km²"

//  ========================= Output ==========================

                              table  =7
 id  name               area  population                density 
  3  Asia           44579000  4545133000      101.9568182328002 
  4  Europe         10180000   742648000       72.9516699410609 
  1  Africa         30370000  1287920000      42.40763911755021 
  6  South America  17840000   428240000     24.004484304932735 
  5  North America  24709000   587615000     23.781415678497712 
  7  Australia       8600000    41261000      4.797790697674419 
  2  Antarctica     14000000        4490  0.0003207142857142857 

Total land area: 150278000 km²

In the background, this table was generated by executing the following compiled SQL code (reformatted):

-- Continent {..., density: population / area} order{ ^density }
WITH subq_1(id, name, area, population, density) AS (
    SELECT id, name, area, population, (CAST(population AS float) / area) AS density
    FROM Continent
    ORDER BY density DESC)
SELECT * FROM subq_1

See more examples in the examples folder.

Interactive Environment



Preql uses an “Interface-Protection Clause” on top of the MIT license.


In simple words, it's free for personal use. Also, it can be used for any commercial or non-commercial purpose, as long as your product doesn't base its value on exposing the Preql language itself to your users. Read more

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