dbt-prql

Original docs at https://github.com/prql/dbt-prql

dbt-prql allows writing PRQL in dbt models. This combines the benefits of PRQL’s power & simplicity within queries, with dbt’s version control, lineage & testing across queries.

Once dbt-prql in installed, dbt commands compile PRQL between {% prql %} & {% endprql %} jinja tags to SQL as part of dbt’s compilation. No additional config is required.

Examples

Simple example

{% prql %}
from employees
filter (age | in 20..30)
{% endprql %}

…would appear to dbt as:

SELECT
  employees.*
FROM
  employees
WHERE
  age BETWEEN 20
  AND 30

Less simple example

{% prql %}
from {{ source('salesforce', 'in_process') }}
derive expected_sales = probability * value
join {{ ref('team', 'team_sales') }} [name]
group name (
  aggregate (expected_sales)
)
{% endprql %}

…would appear to dbt as:

SELECT
  name,
  {{ source('salesforce', 'in_process') }}.probability * {{ source('salesforce', 'in_process') }}.value AS expected_sales
FROM
  {{ source('salesforce', 'in_process') }}
  JOIN {{ ref('team', 'team_sales') }} USING(name)
GROUP BY
  name

…and then dbt will compile the source and refs to a full SQL query.

Replacing macros

dbt’s use of macros has saved many of us many lines of code, and even saved some people some time. But imperatively programming text generation with code like if not loop.last is not our highest calling. It’s the “necessary” part rather than beautiful part of dbt.

Here’s the canonical example of macros in the dbt documentation:

{%- set payment_methods = ["bank_transfer", "credit_card", "gift_card"] -%}

select
order_id,
{%- for payment_method in payment_methods %}
sum(case when payment_method = '{{payment_method}}' then amount end) as {{payment_method}}_amount
{%- if not loop.last %},{% endif -%}
{% endfor %}
from {{ ref('raw_payments') }}
group by 1

Here’s that model using PRQL1, including the prql jinja tags.

{% prql %}
func filter_amount method -> s"sum(case when payment_method = '{method}' then amount end) as {method}_amount"

from {{ ref('raw_payments') }}
group order_id (
  aggregate [
    filter_amount bank_transfer,
    filter_amount credit_card,
    filter_amount gift_card,
  ]
)
{% endprql %}

As well the query being simpler in its final form, writing in PRQL also gives us live feedback around any errors, on every keystroke. Though there’s much more to come, check out the current version on PRQL Playground.

What it does

When dbt compiles models to SQL queries:

  • Any text in a dbt model between {% prql %} and {% endprql %} tags is compiled from PRQL to SQL before being passed to dbt.
  • The PRQL complier passes text that’s containing {{ & }} through to dbt without modification, which allows us to embed jinja expressions in PRQL. (This was added to PRQL specifically for this use-case.)
  • dbt will then compile the resulting model into its final form of raw SQL, and dispatch it to the database, as per usual.

There’s no config needed in the dbt project; this works automatically on any dbt command (e.g. dbt run) assuming dbt-prql is installed.

Installation

pip install dbt-prql

Current state

Currently this is new, but fairly feature-complete. It’s enthusiastically supported — if there are any problems, please open an issue.