Why Column descriptions in dbt? - Purpose & Use Cases

The Big Idea

What if a simple note could save you hours of confusion and mistakes in your data work?

The Scenario

Imagine you have a big spreadsheet with many columns, but none of them have labels or explanations. You and your team spend hours guessing what each column means before you can even start analyzing the data.

The Problem

Without clear descriptions, it's easy to misunderstand data, make mistakes, and waste time asking others for help. This slows down projects and causes frustration when you have to revisit the same unclear data again.

The Solution

Using column descriptions in dbt lets you add clear, simple explanations to each column right where the data lives. This helps everyone understand the data quickly and reduces errors.

Before vs After

✗ Before

select user_id, amt, dt from sales

✓ After

columns:
  - name: user_id
    description: 'Unique ID for each user'
  - name: amt
    description: 'Amount of sale in USD'
  - name: dt
    description: 'Date of the sale'

What It Enables

Clear column descriptions make data trustworthy and easy to use for everyone on your team, speeding up analysis and decision-making.

Real Life Example

A marketing team uses column descriptions to understand customer data quickly, so they can create better campaigns without waiting for data experts to explain each field.

Key Takeaways

Column descriptions explain what each piece of data means.

They save time and reduce mistakes by making data clear.

dbt lets you add these descriptions directly in your data models.

Practice

1. What is the main purpose of adding column descriptions in dbt?

easy

A. To change the data type of columns

B. To create new columns in the model

C. To explain what each column means for better understanding

D. To write SQL queries inside the YAML file

Solution

1. Step 1: Understand the role of column descriptions

   Column descriptions provide explanations about what each column represents in the data model.

2. Step 2: Differentiate from other YAML uses

   They do not change data types, create columns, or contain SQL code; they only describe columns.

3. Final Answer:

   To explain what each column means for better understanding -> Option C

4. Quick Check:

   Column descriptions = explain columns [OK]

Hint: Descriptions explain columns, not change data or structure [OK]

Common Mistakes:

• Thinking descriptions change data types
• Confusing descriptions with SQL code
• Assuming descriptions create new columns

2. Which of the following is the correct syntax to add a column description in a dbt YAML file?

easy

A. description:
customer_id: 'Unique ID for each customer'

B. columns:
- name: customer_id
description: 'Unique ID for each customer'

C. columns:
customer_id: 'Unique ID for each customer'

D. columns:
- customer_id: 'Unique ID for each customer'

Solution

1. Step 1: Recall YAML structure for columns in dbt

   The correct format uses a list under columns: with each item having name and description keys.

2. Step 2: Compare options to correct format

   columns: - name: customer_id description: 'Unique ID for each customer' matches the correct YAML syntax with dash, name, and description keys properly indented.

3. Final Answer:

   columns: - name: customer_id description: 'Unique ID for each customer' -> Option B

4. Quick Check:

   YAML columns list with name and description = columns: - name: customer_id description: 'Unique ID for each customer' [OK]

Hint: Use dash list with name and description keys in YAML [OK]

Common Mistakes:

• Using key-value pairs without dash list
• Putting description outside columns section
• Incorrect indentation or missing name key

3. Given this YAML snippet in a dbt model:

columns:
  - name: order_id
    description: 'Unique order identifier'
  - name: order_date
    description: 'Date when order was placed'

What will dbt show for the order_date column in documentation?

medium

A. No description available

B. Unique order identifier

C. order_date

D. Date when order was placed

Solution

1. Step 1: Locate the description for order_date

   The YAML shows order_date has description 'Date when order was placed'.

2. Step 2: Understand dbt documentation behavior

   dbt uses the description text to show in docs, not the column name or other text.

3. Final Answer:

   Date when order was placed -> Option D

4. Quick Check:

   dbt docs show column description text [OK]

Hint: dbt docs show the description text, not column name [OK]

Common Mistakes:

• Confusing column name with description
• Assuming no description if present
• Picking wrong description text

4. You wrote this YAML for column descriptions but dbt docs shows no descriptions:

columns:
  - name: user_id
    description 'User unique ID'

What is the error causing descriptions not to appear?

medium

A. Missing colon after description key

B. Wrong indentation of columns

C. Missing dash before name

D. Description text should be uppercase

Solution

1. Step 1: Check YAML syntax for description key

   The line description 'User unique ID' is missing a colon after description.

2. Step 2: Understand YAML parsing impact

   Without the colon, YAML is invalid and dbt cannot read the description, so docs show no description.

3. Final Answer:

   Missing colon after description key -> Option A

4. Quick Check:

   YAML keys need colon after them [OK]

Hint: Always put colon after YAML keys like description [OK]

Common Mistakes:

• Forgetting colon after keys
• Incorrect indentation
• Assuming case sensitivity matters

5. You want to add descriptions for multiple columns in a dbt model YAML file. Which approach correctly documents two columns product_id and price with descriptions, ensuring dbt docs will display them properly?

hard

A. columns:
- name: product_id
description: 'ID of the product'
- name: price
description: 'Price in USD'

B. columns:
product_id: 'ID of the product'
price: 'Price in USD'

C. columns:
- product_id: 'ID of the product'
- price: 'Price in USD'

D. columns:
name: product_id
description: 'ID of the product'
name: price
description: 'Price in USD'

Solution

1. Step 1: Recall correct YAML list format for multiple columns

   Each column must be an item in a list with name and description keys.

2. Step 2: Evaluate each option's structure

   columns: - name: product_id description: 'ID of the product' - name: price description: 'Price in USD' correctly uses a list with two items, each having name and description properly indented.

3. Final Answer:

   columns: - name: product_id description: 'ID of the product' - name: price description: 'Price in USD' -> Option A

4. Quick Check:

   List of columns with name and description keys = columns: - name: product_id description: 'ID of the product' - name: price description: 'Price in USD' [OK]

Hint: Use dash list with name and description for each column [OK]

Common Mistakes:

• Using key-value pairs without dash list
• Repeating keys without list items
• Incorrect indentation breaking YAML