Let’s try: dbt part 9 — variables

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[embed]Let's try: dbt part 9 - variables Variables bring flexibility to our pipelines so we define and utilize them here.bluebirz.net

Variables bring flexibility to our pipelines. There are two easy methods to define and utilize variables in dbt.

Set globally

We can declare and define through dbt_project.yml as below.

Define and use

Config in dbt_project.yml can be made under the key vars like this.

vars:
  target_date: 2026-01-01

This is the new variable target_date and then we can refer the variable target_date using var() macro in a model like below.

select *
from {{ source("students", "student_grades") }}
where updated_at = '{{ var("target_date") }}'

When we compile and the value of target_date would be assigned for updated_at like this.

$ dbt compile 
Compiled node 'selected_students' is:
select *
from `bluebirz-playground`.`raw`.`student_grades`
where updated_at = '2026-01-01'

Overriding

There is a case we want to override the variables’ value so with --vars flag the values will be substituted.

$ dbt compile --vars '{target_date: 2026-02-01}'
Compiled node 'selected_students' is:
select *
from `bluebirz-playground`.`raw`.`student_grades`
where updated_at = '2026-02-01'

Double-check the quotes and escape characters for the YAML configs and flag --vars.

Default value

In some cases, we need default values for variables. Supplying second argument to var() macro is giving default values.

select *
from {{ source("students", "student_grades") }}
where
    updated_at = '{{ var("target_date") }}'
    and name = '{{ var("target_name", "Billy") }}'

Now Billy is a default value when target_name can't be found like this.

$ dbt compile 
Compiled node 'selected_students' is:
select *
from `bluebirz-playground`.`raw`.`student_grades`
where
    updated_at = '2026-01-01'
    and name = 'Billy'

Dealing with arrays

We can define an array in YAML syntax using hyphens (-) or brackets ([]) as below.

vars:
  target_date: 2026-01-01
  target_subjects:
    - "biology"
    - "physics"
    - "chemistry"
  other_subjects: ["literature", "mathematics"]

Now let’s say we want this final query below as a model.

$ dbt compile 
Compiled node 'selected_students' is:
select *
from `bluebirz-playground`.`raw`.`student_grades`
where
    updated_at = '2026-01-01'
    and subject in ('biology', 'physics', 'chemistry')

There are different ways to achieve it.

• loop

We can do it in traditional loop way. With iterating over an array using for-loop, concatenating each element in it with comma , if the element isn’t the last in the array, and we can explicitly get a complete string having commas from that array.

select *
from {{ source("students", "student_grades") }}
where
    updated_at = '{{ var("target_date") }}'
    and subject in (
        {%- for subject in var("target_subjects") -%}
            '{{ subject }}' {%- if not loop.last -%},{%- endif -%}
        {%- endfor -%}
    )

• replace

By default, an array can be cast to a string in format [a, b, c, ...], so we can just using Jinja filter [replace](https://jinja.palletsprojects.com/en/stable/templates/#jinja-filters.replace) to transform [] to ().

select *
from {{ source("students", "student_grades") }}
where
    updated_at = '{{ var("target_date") }}'
    and subject in {{ var("target_subjects") | replace("[", "(") | replace("]", ")") }}

• join

Or just a Jinja filter [join](https://jinja.palletsprojects.com/en/stable/templates/#jinja-filters.join) to combine all elements with commas and surround them with quotes and parentheses ('...') then we now get a complete string.

select *
from {{ source("students", "student_grades") }}
where
    updated_at = '{{ var("target_date") }}'
    and subject in ('{{ var("target_subjects") | join("', '") }}')

Set locally

In case we don’t want to declare it globally but just have some to use in a single model, we can do this.

Set and use

Using {% set <variable> = <value> %} to declare a variable and its value in the model. Then refer the variables just by writing statement {{ <var> }}.

{%- set target_date = "2026-01-01" -%}

select *
from {{ source("students", "student_grades") }}
where updated_at = '{{ target_date }}'

Now target_date is "2026-01-01" after compiling.

$ dbt compile
Compiled node 'selected_students' is:
select *
from `bluebirz-playground`.`raw`.`student_grades`
where updated_at = '2026-01-01'

Set arrays

Also declare arrays and concatenate it to string like above examples.

{%- set target_date = "2026-01-01" -%}
{%- set target_subjects = ["biology", "physics", "chemistry"] -%}
select *
from {{ source("students", "student_grades") }}
where
    updated_at = '{{ target_date }}'
    and subject in {{ target_subjects | replace("[", "(") | replace("]", ")") }}

Now we get the array like this.

$ dbt compile
Compiled node 'selected_students' is:
select *
from `bluebirz-playground`.`raw`.`student_grades`
where
    updated_at = '2026-01-01'
    and subject in ('biology', 'physics', 'chemistry')

Overriding from global vars

And of course, defining local variables by inheriting global variables is also possible.

{%- set search_date = var("target_date") -%}
select *
from {{ source("students", "student_grades") }}
where updated_at = '{{ search_date }}'

Then --vars flag is usable here.

$ dbt compile --vars '{target_date: 2026-02-01}'
Compiled node 'selected_students' is:
select *
from `bluebirz-playground`.`raw`.`student_grades`
where updated_at = '2026-02-01'

Wrap up

• Define global variables with key vars in dbt_project.yml.
• Utilize global variables by {{ var("<var>", "<default_value>") }}.
• Define local variables with {% set <var> = <value> %} in a model.
• Utilize local variables by {{ <var> }}.
• Flag --vars is for overriding variables when execute dbt commands.
• Jinja filters like replace, join and for-loop are useful for array concatenation.

References

• About var function | dbt Developer Hub
• About set context method | dbt Developer Hub
• List of Builtin Filters — Template Designer Documentation — Jinja Documentation