[Yandex Cloud documentation](../../index.md) > [Yandex DataLens](../index.md) > Troubleshooting > [FAQ](index.md) > Calculated fields

# Calculated fields


### How do I calculate a cumulative sum? {#how-to-calculate-cumulative-sum}

Use the [RSUM](../function-ref/RSUM.md) function.

### Why do IFNULL and ZN functions return NULL? {#why-ifnull-zn-are-null}

The [IFNULL](../function-ref/IFNULL.md) and [ZN](../function-ref/ZN.md) functions may return `NULL` if their arguments take the `NaN` value.