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# Add columns through Lookup

> Use Lookup in Sigma to connect related columns between data elements and inject matching data from one into another.

A *Lookup* is an action that allows you to connect related columns between two data elements, injecting the data from one element into another. The two elements are joined by a pair of columns — one from each element — that share common values. We call these joining columns *join keys*.

Columns created from a lookup can be added using the [Lookup function](/docs/lookup). However, you can also add a new lookup column without explicitly writing a formula. This second option is documented below.

## Requirements

* To use this feature, you must have **Can Edit** or **Can Explore** [access](/docs/folder-and-document-permissions#document-permissions) to the individual workbook.

## Add a column through Lookup

#### **Prerequisites**:

* You will need at least two data elements — one to join to and one to join from
* Both elements must live in the same workbook
* Both elements must be sourced from the same connection
* The element you are joining to must not be a child of the element you are joining from

### Add a Column via Lookup

**Before you start:** This action is only available in edit mode. To begin editing, click **Edit** in the top right corner of the page.

1. Select the data element that you want to add a column to.
2. Click the caret icon next to any column’s name to open its menu.
3. Select **Add column via lookup**.
   This will open the **Add Lookup** modal.
   * The first section, **Which column would you like to add?**, will prompt you to select:
     * A source element
     * A column, from the source element, to use in your new column
     * \[optional] An aggregate value to apply to the column
   * The second section, **Map two elements**, will prompt you to define one or more sets of join keys.
4. Under **Select element**, select your source element.
   Elements are organized by their workbook pages.
5. Under Column to add, select the column you want to use in your new column.
6. \[optional] Under aggregate, select an aggregate function to apply to the column’s values.
   <br />***Note***: Under the hood, aggregation turns the Lookup into a Rollup.\*
7. Under **Map two elements**, select a column from each data element to use as a join key.
8. \[optional] To add additional pairs of join keys, click **+add another mapping** and repeat step 7.

## Related resources

* [Intro to data elements](/docs/intro-to-data-elements)
* [Lookup](/docs/lookup)
* [Rollup](/docs/rollup)