Tableau Course
Data Types in Tableau
Every field in your dataset has a data type — and Tableau treats each type differently when you drag it onto a shelf, write a calculation, or build a chart. Getting data types right is one of the most important habits to build early.
The Five Data Types in Tableau
Tableau recognises five core data types. Each one carries a distinct icon in the Data pane, and each one behaves differently when placed on a shelf or used in a formula.
Any combination of letters, numbers, and symbols stored as plain text. Tableau cannot perform arithmetic on strings — it can only group, filter, and label with them. Examples: Category, Customer Name, Order ID, Region.
Numeric values that can be aggregated — summed, averaged, counted, or used in calculations. Tableau further splits numbers into integers and decimals. Examples: Sales, Profit, Quantity, Discount.
Date fields unlock Tableau's built-in date hierarchy — Year, Quarter, Month, Week, Day — allowing you to drill down into any time period with a single click. Examples: Order Date, Ship Date, Hire Date.
A field with only two possible values — True or False. Booleans are useful for filtering and segmenting data. Examples: Returned, Is New Customer, Discount Applied.
A string or number field that Tableau has recognised as a location — country, state, city, or postal code. Geographic fields can be plotted directly onto a map. Examples: Country, State, City, Postal Code.
Data Types in the Data Pane
Here is how the five data types look inside a real Tableau Data pane, using the Superstore dataset as the example:
Discrete vs Continuous — The Blue and Green Pill
Inside Tableau, every field placed on a shelf appears as either a blue pill or a green pill. This is not just a colour — it controls how Tableau draws the axis and segments the data.
Creates a header — a distinct label for each category value. The axis shows individual buckets: East, West, North, South. Used by default for Dimensions.
Creates an axis — a continuous numerical scale from a minimum to a maximum value. Used by default for Measures. The axis shows a range: 0 to 500,000.
A field does not have to stay in its default state. Right-click any field on a shelf and you will see options to convert it between Discrete and Continuous. A common example is Order Date — by default it is discrete (showing individual year labels), but switching it to continuous creates a smooth timeline axis instead.
How Date Fields Behave in Tableau
Date fields deserve extra attention because they behave differently from every other type. When you drag a date field onto the Columns shelf, Tableau does not just show a list of dates — it automatically groups them by Year and gives you a hierarchy you can expand.
| Date Level | Example Output | When to Use |
|---|---|---|
| Year | 2021, 2022, 2023 | High-level trend comparison across years |
| Quarter | Q1, Q2, Q3, Q4 | Seasonal patterns within a year |
| Month | January, February… December | Monthly performance tracking |
| Week | Week 1, Week 2… | Weekly operations or campaigns |
| Day | 1, 2, 3… 31 | Daily granularity for short time ranges |
Right-clicking a date field on a shelf shows a full list of date levels. You can switch between them at any time — no need to create separate fields for each level in your source data.
Changing a Data Type in Tableau
Tableau sometimes misreads a field's data type — especially when connecting to CSV files or messy Excel sheets. There are two places to fix this:
A Practical Example — Superstore Data Types
Here is a sample of the Superstore dataset with each column's data type labelled, so you can see how a real table maps to Tableau's five types:
| Field Name | Sample Value | Data Type | Dimension / Measure |
|---|---|---|---|
| Order ID | CA-2023-001 | Abc | Dimension |
| Order Date | 01/03/2023 | 📅 Date | Dimension |
| Category | Furniture | Abc | Dimension |
| State | California | 🌐 Geo | Dimension |
| Sales | 1,200.00 | # Number | Measure |
| Quantity | 3 | # Number | Measure |
| Returned | True / False | T|F | Dimension |
Common Data Type Mistakes to Avoid
These are the three data type errors that trip up beginners most often in Tableau:
Tableau strips leading zeros from codes like 01234, turning them into 1234. Always store postal codes as strings.
If Sales contains a currency symbol in the source file, Tableau reads it as text and SUM(Sales) returns zero. Remove symbols from source data or change the type to Number.
Dates stored as text cannot use Tableau's date hierarchy. You lose the ability to group by Year, Quarter, or Month. Always store dates in a recognised date format.
The Discrete vs Continuous distinction is one of the concepts beginners find confusing at first — because the same field can appear as either depending on how you use it. A simple rule to remember: blue pills create headers and labels; green pills create axes and scales. When a chart does not look right, the first thing to check is whether your fields are discrete or continuous. Right-clicking a field on a shelf and toggling between the two options will often fix the issue immediately.
Practice Questions
1. A Postal Code field is being stored as a number in Tableau and losing its leading zeros. Which data type should it be changed to?
2. A green pill on a Tableau shelf means the field is being treated as which type?
3. When you drag a Date field onto the Columns shelf in Tableau, which date level does it default to?
Quiz
1. What does a blue (Discrete) field on a Tableau shelf produce in the view?
2. A field called Returned contains only the values True and False. Which Tableau data type does this field belong to?
3. How can you change a field's data type from within a Tableau worksheet without returning to the Data Source tab?
Next up — Lesson 6: Dimensions and Measures in depth — how Tableau classifies every field, and how to override its decisions when it gets them wrong.