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> For a complete documentation index, see https://help.sigmacomputing.com/docs/join-functions/llms.txt.
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# Join functions

> Browse Sigma join functions available in formulas and calculations.

Join functions retrieve data from target elements based on related columns in the local and target elements.

| Function                                   | Description                                                                                                                                              |
| :----------------------------------------- | :------------------------------------------------------------------------------------------------------------------------------------------------------- |
| [Lookup](/docs/lookup)                     | Finds a value in a specified target element column and returns the corresponding row value from another column in that element.                          |
| [LookupMatchNulls](/docs/lookupmatchnulls) | Finds a value in a specified target element column and returns the corresponding row value from another column in that element, matching null join keys. |
| [Rollup](/docs/rollup)                     | Finds a value in a specified target element column and aggregates all corresponding row values from another column in that element.                      |

> Official documentation and guidance for using Sigma to build AI apps, dashboards, and agents on governed warehouse data.

## Docs

- [Lookup](https://help.sigmacomputing.com/docs/lookup.md): Use the Sigma Lookup function to find matching data inside a data element, either in the same table, or in an external table.
- [LookupMatchNulls](https://help.sigmacomputing.com/docs/lookupmatchnulls.md): Use the Sigma LookupMatchNulls function to find matching data in another data element, including rows where both join keys are null.
- [Rollup](https://help.sigmacomputing.com/docs/rollup.md): Use the Sigma Rollup function to perform a lookup and return an aggregation.