Rollups: Summarizing Related Data

1. What is a Rollup?

A rollup is a property that works in tandem with a relation. It pulls data from the pages linked in a relation property and then applies a calculation to that data.

Think of it like this:

• A Relation creates the pathway between two databases.
• A Rollup sends a request down that pathway to fetch and summarize information.

A critical point to remember is that you must have a Relation property set up before you can create a Rollup.

To get a clear definition, let's watch a short clip that introduces the concept.

The 3-Step Rollup Configuration

Whenever you create a rollup, you will configure it in three steps:

1. RELATION: Choose the relation property you want to pull data from.
2. PROPERTY: Choose the specific property (e.g., 'Status', 'Due Date', 'Budget') from the related database.
3. CALCULATE: Choose the calculation you want to perform on that property's data (e.g., 'Sum', 'Count', 'Average').

2. Your First Rollup: Summing Numerical Data

Let's start with a classic project management scenario. Your Tasks database has individual time estimates, and you want your Projects database to show the total estimated time for each project automatically. This is a perfect job for a rollup using the Sum calculation.

The official Notion team has a concise video demonstrating exactly this.

This automatic summation is a huge time-saver and a core feature in many project management templates. Instead of manually adding up task hours, the project overview is always up-to-date.

3. A Powerful Use Case: Calculating Project Progress

One of the most visually appealing and useful features in a sellable template is an automated progress bar. This is achieved with a rollup that calculates the percentage of completed tasks.

Here’s the logic:

1. Your Tasks database has a Checkbox property (e.g., "Done").
2. Your Projects database has a Relation to the Tasks.
3. You create a Rollup property in Projects that looks at the Done checkbox in the related tasks and calculates the "Percent checked".

This creates a dynamic progress bar that updates in real-time as you check off tasks. Let's watch a detailed walkthrough of this concept being applied to a habit tracker, which uses the exact same principles.

4. Exploring the Range of Rollup Calculations

As you've seen, rollups can do more than just Sum and Percent checked. Notion provides a wide range of calculations to handle different data types. To get a full overview of the possibilities, it's best to consult the official documentation.

As a quick summary, rollup calculations fall into a few key categories:

• General: Show original values, count items, or show percentages of empty/filled properties.
• Number-specific: Sum, Average, Median, Min, Max, Range.
• Date-specific: Earliest date, Latest date, Date range.

Knowing these options allows you to build much more informative dashboards for your future clients.

✍️ Exercise: Enhance Your Project Manager

It's time to apply what you've learned. Let's go back to the "My First Connected System" you built in the previous lesson and add some powerful rollups.

Part 1: Enhance the Tasks Database

• Navigate to the Tasks database you created.
• Add a Number property and name it Time (hours). For the number format, choose "Number".
• Add a Checkbox property and name it Done.
• Add some values: Assign 2, 5, and 3 hours respectively to your three tasks.

Part 2: Create Your Rollups in the Projects Database

• Navigate to your Projects database.
• Add a new property. Name it Total Hours.
• For the property type, select Rollup.
• Configure the rollup:
  • Relation: Select your Tasks relation.
  • Property: Select Time (hours).
  • Calculate: Select Sum.
• You should now see the total hours for each project calculated automatically!

Part 3: Add the Progress Bar

• In the Projects database, add another new property. Name it Progress.
• Select the Rollup property type.
• Configure the rollup:
  • Relation: Select your Tasks relation.
  • Property: Select Done.
  • Calculate: Select Percent checked.
• Click on the property name (Progress) and change how it's displayed. Choose "Bar" for the "Show as" option.

Part 4: Test Your System

• Go back to your Tasks database and check the "Done" box for one of the tasks.
• Return to your Projects database. Observe how the Progress bar has updated automatically. Congratulations, you've built an automated project tracker!

Lesson Summary and Next Steps

Excellent work! You've now mastered Rollups, moving beyond simple data linking to performing powerful, automatic calculations. This ability to aggregate data is what turns a simple collection of lists into an intelligent, responsive system.

Key Takeaways:

• Rollups require Relations: You can't have a rollup without a relation to provide the data pathway.
• Three-Step Configuration: Setting up a rollup always involves choosing the Relation, the Property to pull from, and the Calculation to perform.
• Powerful Summaries: Rollups are the key to creating high-level dashboards with features like total budget calculations, task counts, and dynamic progress bars.

Rollups are fantastic for a set of predefined calculations. But what happens when you need more custom logic? What if you want to combine text from multiple properties, display different outputs based on a condition (an "if" statement), or perform a mathematical operation that isn't on the rollup list?

For that, we need an even more flexible tool. In our next lesson, we will dive into Formulas, unlocking the next level of customization and intelligence for your Notion databases.