Variables and control flow in dbt - Step-by-Step Execution

Concept Flow - Variables and control flow

Start

↓

Set Variable

↓

Check Condition

↓

Execute Block

↓

Update Variable or End

↩Back to Check or End

This flow shows how dbt sets variables, checks conditions, executes code blocks based on conditions, and updates variables or ends.

Execution Sample

dbt

{% set my_var = 0 %}

{% if my_var < 2 %}
  {{ log('Variable is less than 2') }}
{% endif %}

This dbt snippet sets a variable and uses an if condition to log a message if the variable is less than 2.

Execution Table

Step	Action	Variable 'my_var'	Condition 'my_var < 2'	Branch Taken	Output
1	Initialize variable 'my_var'	0	N/A	N/A	Variable set to 0
2	Evaluate condition 'my_var < 2'	0	True	Yes	Log message: 'Variable is less than 2'
3	End of control flow	0	N/A	N/A	Execution stops

💡 Reached end of code after condition check and logging

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
my_var	undefined	0	0	0

Key Moments - 2 Insights

Why does the condition 'my_var < 2' evaluate to True when 'my_var' is 0?

Because 0 is less than 2, the condition is True as shown in execution_table row 2, so the code inside the if block runs.

What happens if the variable 'my_var' was 3 instead of 0?

The condition 'my_var < 2' would be False, so the branch taken would be No, skipping the log message. This is shown by the condition check logic in execution_table.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'my_var' at Step 2?

A 2

B 0

C 1

D undefined

💡 Hint

Check the 'Variable my_var' column at Step 2 in the execution_table.

At which step does the condition 'my_var < 2' get evaluated?

A Step 2

B Step 1

C Step 3

D No step

💡 Hint

Look at the 'Condition' column in the execution_table to find when it is evaluated.

If 'my_var' was set to 3, what would happen at Step 2?

A Condition True, log message printed

B Error occurs

C Condition False, log message skipped

D Variable changes to 0

💡 Hint

Refer to key_moments explanation about variable values and condition outcomes.

Concept Snapshot

dbt variables store values used in control flow.
Use {% if name < value %} to check conditions.
Code inside if runs only if condition is True.
Variables do not change unless explicitly updated.
Control flow ends after last statement.

Full Transcript

In dbt, variables hold values that control the flow of code. We start by setting a variable, like 'my_var' to 0. Then we check if 'my_var' is less than 2. Since 0 is less than 2, the condition is True, so the code inside the if block runs and logs a message. If the variable was 3, the condition would be False and the code inside the if block would be skipped. Variables keep their values unless changed. The flow ends after the last statement.