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# Warnings about IDs, currency and percentages in Mammoth

> Every Mammoth warning a column's meaning triggers: summing an ID, adding percentages, mixing money and percent, and ranking IDs, with what each offers.
>
> Applies to: Where: Explore card, Group & Pivot, Create Metric, Math Function, Window Function, Join, Lookup, Unpivot

When a column is marked as an ID, a currency or a percentage, Mammoth questions choices that are probably a mistake, such as summing order IDs. The warnings never block **Apply**. To set or change a column's meaning, see [Column types, IDs, currency and percentages](https://mammoth.io/docs/learn/clean-and-shape/column-types/).

## Every warning and where it appears

Summing or averaging an ID adds up codes, and summing percentages rarely means anything, so some functions question a choice that is probably a mistake. Each warning starts with the column name in bold, such as "**order_id is an ID.**" None of them blocks **Apply**.

| Where | Warning | When |
| --- | --- | --- |
| Explore card **Show values by**, **Group & Pivot** task | "Adding or averaging it adds up the codes. Did you mean Count distinct?" | Sum or Average of an ID column. Group & Pivot offers **Swap to Count distinct** or **Keep**. |
| Explore card **Show values by**, **Group & Pivot** task | "Adding percentages rarely means anything. Did you mean Average?" | Sum of a Percentage column. Group & Pivot offers **Swap to Average** or **Keep**. |
| **Create Metric** from a column header | "Sum adds up the codes." or "Average of the codes is not a quantity." | Sum or Average of an ID column |
| **Create Metric** from a column header | "Adding percentages rarely means anything. Average usually does." | Sum of a Percentage column |
| Math Function | "IDs are labels, not amounts, so doing arithmetic on them isn't meaningful." | A formula (in Formula mode) uses an ID column. |
| Math Function | "This formula mixes an amount of money with a percentage. Check that the result is what you mean." | A formula (in Formula mode) uses a Currency and a Percentage column together. |
| Window Function | "IDs are labels, not amounts, so a running total or ranking of them isn't meaningful." | A sum, average or ranking runs over an ID column. |
| Join, Lookup | Key type and meaning warnings | The keys are stored as different types, one is an ID and the other isn't, or they are in different currencies. See [Join two datasets on a shared column](https://mammoth.io/docs/learn/clean-and-shape/join/). |
| Unpivot | "The new value column does not carry over the meaning of the columns you stack (an ID, a currency or a percentage). It starts as a plain column." | A stacked column has a meaning. |

In Group & Pivot, **Keep** dismisses the warning for that aggregation and keeps your choice. When you pick a column for Sum or Average in an Explore card, ID columns are listed last with the hint "it's an ID". [Data Check](https://mammoth.io/docs/learn/clean-and-shape/duplicates-and-checks/) also suggests checks for ID, Percentage and Currency columns.

## Related

- [Column types, IDs, currency and percentages](https://mammoth.io/docs/learn/clean-and-shape/column-types/): change a column's type or meaning.
- [Group, pivot and unpivot](https://mammoth.io/docs/learn/clean-and-shape/group-and-pivot/): where the Sum and Average warnings appear.
- [Calculate with formulas](https://mammoth.io/docs/learn/clean-and-shape/formulas/): Math Function and Window Function warnings.

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Source: https://mammoth.io/docs/learn/clean-and-shape/column-type-warnings.md · Updated: 2026-11-08