DBT Macros & Jinja Flashcards

What does `{# This is a comment #}` do in a dbt SQL file?

Answer: Creates a Jinja comment stripped from compiled SQL

Jinja comments (`{# ... #}`) are stripped entirely during compilation and do not appear in the generated SQL sent to the warehouse.

Which dbt macro generates a series of comma-separated column expressions from a list?

Answer: dbt_utils.star()

`dbt_utils.star()` selects all columns from a relation, optionally excluding specified ones, and renders them as a comma-separated list.

What happens if you call `{{ var('my_var') }}` and `my_var` is not defined anywhere?

Answer: dbt raises a compilation error

If a variable is referenced without a default and is not defined in dbt_project.yml or via `--vars`, dbt raises a compilation error.

In dbt, what is a 'dispatch' namespace used for in macro resolution?

Answer: Allowing packages to override built-in macros with adapter-specific versions

The dispatch namespace system lets packages like dbt-utils provide adapter-specific macro overrides that dbt resolves at compile time via `adapter.dispatch()`.

Which Jinja statement would you use to set a local variable inside a dbt model?

Answer: {% set my_var = 'value' %}

`{% set variable_name = value %}` is the Jinja statement for assigning a value to a local variable within a template.

What does `{{ dbt_utils.union_relations(relations=[ref('a'), ref('b')]) }}` do?

Answer: UNIONs all columns from multiple relations into a single result set

`dbt_utils.union_relations()` generates a UNION ALL query across a list of relations, aligning columns by name and filling missing ones with NULLs.