How to Use For Loop in Jinja with dbt: Simple Guide

In dbt, you use a for loop in Jinja by writing {% for item in list %}...{% endfor %} to repeat code blocks dynamically. This helps generate SQL code based on lists or dictionaries inside your dbt models or macros.

Syntax

The for loop in Jinja starts with {% for variable in sequence %} and ends with {% endfor %}. Inside the loop, you can use the variable to access each item in the sequence.

• variable: name for each item in the loop
• sequence: list or dictionary to loop over
• {% endfor %}: marks the end of the loop

jinja

{% for item in my_list %}
  -- use {{ item }} here
{% endfor %}

Example

This example shows how to loop over a list of column names to select them dynamically in a dbt model using Jinja.

jinja

{% set columns = ['id', 'name', 'email'] %}

select
{% for col in columns %}  {{ col }}{% if not loop.last %}, {% endif %}
{% endfor %}
from users

Output

select
  id, name, email
from users

Common Pitfalls

Common mistakes when using for loops in Jinja with dbt include:

• Forgetting to close the loop with {% endfor %}.
• Not handling commas or separators properly, which can cause invalid SQL.
• Using {{ }} instead of {% %} for control statements like loops.

jinja

{% for col in columns %}
  {{ col }}
{% endfor %}  -- Missing commas between columns

-- Correct way:
{% for col in columns %}{{ col }}{% if not loop.last %}, {% endif %}{% endfor %}

Quick Reference

Syntax	Description
{% for item in list %} ... {% endfor %}	Loop over each item in a list or sequence
{{ variable }}	Print the value of a variable inside the loop
loop.index	Current loop iteration starting at 1
loop.last	True if current item is the last in the loop
{% if condition %} ... {% endif %}	Conditional logic inside loops

Key Takeaways

Use {% for item in list %} ... {% endfor %} to loop in Jinja within dbt.

Remember to close loops with {% endfor %} to avoid syntax errors.

Use loop.last to handle separators like commas correctly in SQL.

Use {% %} for control flow and {{ }} to print variables inside loops.

For loops help generate dynamic SQL code based on lists or dictionaries.