if/else logic in models in dbt - Step-by-Step Execution

Concept Flow - if/else logic in models

Start

↓

Evaluate condition

↓

Execute IF block

↓

Execute ELSE block

↓

Continue with rest of model

The model checks a condition. If true, it runs the IF part; otherwise, it runs the ELSE part, then continues.

Execution Sample

dbt

select
  case
    when sales > 100 then 'High'
    else 'Low'
  end as sales_category
from sales_data

This SQL code classifies sales as 'High' if sales are over 100, otherwise 'Low'.

Execution Table

Row	sales	Condition (sales > 100)	Branch Taken	Output sales_category
1	150	True	IF	'High'
2	90	False	ELSE	'Low'
3	100	False	ELSE	'Low'
4	200	True	IF	'High'
5	50	False	ELSE	'Low'

💡 All rows processed; condition evaluated for each row to assign category.

Variable Tracker

Variable	Row 1	Row 2	Row 3	Row 4	Row 5
sales	150	90	100	200	50
Condition (sales > 100)	True	False	False	True	False
sales_category	'High'	'Low'	'Low'	'High'	'Low'

Key Moments - 2 Insights

Why does sales = 100 result in 'Low' and not 'High'?

Because the condition is sales > 100, which means strictly greater than 100. At 100, the condition is False, so ELSE branch runs (see execution_table row 3).

What happens if the condition is True for a row?

The IF block runs, assigning 'High' to sales_category (see execution_table rows 1 and 4).

Visual Quiz - 3 Questions

Look at the execution table, what is sales_category for row 2?

A 'High'

B 'Low'

C NULL

D 'Medium'

💡 Hint

Check row 2 in execution_table under 'Output sales_category'

At which row does the condition sales > 100 become False for the first time?

A Row 1

B Row 3

C Row 2

D Row 5

💡 Hint

Look at 'Condition (sales > 100)' column in execution_table

If the condition changed to sales >= 100, what would sales_category be for row 3?

A 'High'

B 'Low'

C NULL

D 'Medium'

💡 Hint

Consider how changing > to >= affects condition for sales = 100 in variable_tracker

Concept Snapshot

if/else logic in dbt models uses SQL CASE statements.
Syntax: CASE WHEN condition THEN result ELSE other_result END.
Evaluates condition row-by-row.
Runs THEN part if True, ELSE part if False.
Useful for categorizing or branching logic in models.

Full Transcript

In dbt models, if/else logic is done using SQL CASE statements. The model checks a condition for each row. If the condition is true, it runs the THEN part; otherwise, it runs the ELSE part. For example, classifying sales as 'High' if sales are greater than 100, else 'Low'. The execution table shows each row's sales value, condition result, branch taken, and output category. Note that sales exactly 100 is not greater than 100, so it falls into the ELSE branch. This logic helps create categories or decisions inside your data models.