---
title: Joining pre-aggregations with different refresh cadences
description: Use a rollup join to combine a heavy, slowly-refreshed fact pre-aggregation with a lightweight, frequently-refreshed lookup pre-aggregation so derived metrics stay fresh without rebuilding the full fact table.
---

## Use case

A common modeling problem is computing a metric that depends on two inputs
which change at very different rates:

- A **large fact table** that is expensive to aggregate and only needs to be
  refreshed on a slow cadence (for example, daily or hourly).
- A **small lookup table** whose values are applied to each fact row and that
  needs to be refreshed much more frequently than the fact aggregation.

Some examples of this pattern:

- Converting an amount column to a target currency using the latest foreign
  exchange (FX) rates — either a single-currency column multiplied by a rate,
  or an `amount` and `currency` column resolved with a `CASE` statement.
- Re-pricing inventory or order lines with a frequently-updated price list.
- Applying a frequently-tuned scoring weight, tax rate, or commission rate to
  historical events.

Combining both inputs into a single [rollup](/reference/data-modeling/pre-aggregations#rollup)
forces the entire pre-aggregation to refresh whenever the lookup values
change, which is wasteful. In the recipe below, we'll learn how to use a
[rollup join](/reference/data-modeling/pre-aggregations#rollup_join) to keep
each pre-aggregation on its own refresh schedule while still serving the
combined, derived query from pre-aggregations.

We'll walk through the FX conversion variant as a concrete example, but the
same pattern applies to any of the use cases above.

<Warning>
  `rollup_join` has several constraints documented on the
  [pre-aggregations reference page](/reference/data-modeling/pre-aggregations#rollup_join).
  In particular: it is currently in Preview, it is designed for joining data
  across data sources, it can only join two rollups, and it is ephemeral —
  set freshness controls on the referenced rollups rather than on the
  `rollup_join` itself.

  The rollup on the right side of the join is also bounded by the number of
  physical Cube Store partitions it can have, which depends on your Cube
  Store compute tier. Note that these are Cube Store physical partitions —
  not Cube logical partitions.
</Warning>

## Data modeling

We have two cubes: `orders`, which stores per-order amounts in the original
transaction currency, and `fx_rates`, which stores the latest exchange rate
from each currency to USD.

The `orders` table looks like this:

| id | currency | amount  | created_at          |
|----|----------|---------|---------------------|
| 1  | EUR      | 120.00  | 2026-05-18 09:14:22 |
| 2  | GBP      | 75.50   | 2026-05-18 11:02:47 |
| 3  | EUR      | 245.10  | 2026-05-19 08:31:05 |
| 4  | USD      | 310.00  | 2026-05-19 10:18:33 |
| 5  | GBP      | 89.99   | 2026-05-19 12:44:51 |

The `fx_rates` table looks like this:

| currency | rate_to_usd |
|----------|-------------|
| EUR      | 1.085       |
| GBP      | 1.262       |
| USD      | 1.000       |

First, define a `rollup` pre-aggregation on `orders` that aggregates the
amount by `currency` and day. This is the heavy pre-aggregation, so we set a
slow `refresh_key` — for example, every day:

<CodeGroup>

```yaml title="YAML"
cubes:
  - name: orders

    sql_table: public.orders

    joins:
      - name: fx_rates
        sql: "{CUBE}.currency = {fx_rates.currency}"
        relationship: many_to_one

    dimensions:
      - name: id
        sql: id
        type: number
        primary_key: true

      - name: currency
        sql: currency
        type: string

      - name: created_at
        sql: created_at
        type: time

    measures:
      - name: amount
        sql: amount
        type: sum

    pre_aggregations:
      - name: orders_rollup
        type: rollup
        measures:
          - amount
        dimensions:
          - currency
        time_dimension: created_at
        granularity: day
        refresh_key:
          every: 1 day
        indexes:
          - name: currency_index
            columns:
              - currency
```

```javascript title="JavaScript"
cube(`orders`, {
  sql_table: `public.orders`,

  joins: {
    fx_rates: {
      sql: `${CUBE}.currency = ${fx_rates.currency}`,
      relationship: `many_to_one`
    }
  },

  dimensions: {
    id: {
      sql: `id`,
      type: `number`,
      primary_key: true
    },

    currency: {
      sql: `currency`,
      type: `string`
    },

    created_at: {
      sql: `created_at`,
      type: `time`
    }
  },

  measures: {
    amount: {
      sql: `amount`,
      type: `sum`
    }
  },

  pre_aggregations: {
    orders_rollup: {
      type: `rollup`,
      measures: [amount],
      dimensions: [currency],
      time_dimension: created_at,
      granularity: `day`,
      refresh_key: {
        every: `1 day`
      },
      indexes: {
        currency_index: {
          columns: [currency]
        }
      }
    }
  }
})
```

</CodeGroup>

Next, define a `rollup` pre-aggregation on `fx_rates`. This pre-aggregation is
small (one row per currency) and cheap to rebuild, so we give it a much
faster `refresh_key` than the orders rollup — for example, every hour:

<CodeGroup>

```yaml title="YAML"
cubes:
  - name: fx_rates

    sql_table: public.fx_rates

    dimensions:
      - name: currency
        sql: currency
        type: string
        primary_key: true

      - name: rate_to_usd
        sql: rate_to_usd
        type: number

    pre_aggregations:
      - name: fx_rates_rollup
        type: rollup
        dimensions:
          - currency
          - rate_to_usd
        refresh_key:
          every: 1 hour
        indexes:
          - name: currency_index
            columns:
              - currency
```

```javascript title="JavaScript"
cube(`fx_rates`, {
  sql_table: `public.fx_rates`,

  dimensions: {
    currency: {
      sql: `currency`,
      type: `string`,
      primary_key: true
    },

    rate_to_usd: {
      sql: `rate_to_usd`,
      type: `number`
    }
  },

  pre_aggregations: {
    fx_rates_rollup: {
      type: `rollup`,
      dimensions: [currency, rate_to_usd],
      refresh_key: {
        every: `1 hour`
      },
      indexes: {
        currency_index: {
          columns: [currency]
        }
      }
    }
  }
})
```

</CodeGroup>

<Note>
  Both pre-aggregations must include an index on the join key (`currency` in
  this example) for the `rollup_join` to match. The `fx_rates_rollup` also
  needs `rate_to_usd` as a dimension so it's available downstream.
</Note>

Finally, define a `rollup_join` pre-aggregation on `orders` that references
both rollups. This is an ephemeral pre-aggregation — it doesn't materialize
its own data, so it doesn't need a `refresh_key`. Cube serves queries from it
by joining the two underlying rollups on the fly:

<CodeGroup>

```yaml title="YAML"
cubes:
  - name: orders
    # ...

    pre_aggregations:
      # ...

      - name: orders_with_fx_rollup
        type: rollup_join
        measures:
          - amount
        dimensions:
          - currency
          - fx_rates.rate_to_usd
        time_dimension: created_at
        granularity: day
        rollups:
          - fx_rates.fx_rates_rollup
          - orders_rollup
```

```javascript title="JavaScript"
cube(`orders`, {
  // ...

  pre_aggregations: {
    // ...

    orders_with_fx_rollup: {
      type: `rollup_join`,
      measures: [amount],
      dimensions: [currency, fx_rates.rate_to_usd],
      time_dimension: created_at,
      granularity: `day`,
      rollups: [fx_rates.fx_rates_rollup, orders_rollup]
    }
  }
})
```

</CodeGroup>

To expose the USD-converted amount, add a derived measure on `orders` that
multiplies the order amount by the FX rate from the joined cube:

<CodeGroup>

```yaml title="YAML"
cubes:
  - name: orders
    # ...

    measures:
      # ...

      - name: amount_usd
        sql: "{CUBE.amount} * {fx_rates.rate_to_usd}"
        type: number
```

```javascript title="JavaScript"
cube(`orders`, {
  // ...

  measures: {
    // ...

    amount_usd: {
      sql: `${CUBE.amount} * ${fx_rates.rate_to_usd}`,
      type: `number`
    }
  }
})
```

</CodeGroup>

## Query

Let's query daily sales in USD by currency:

```json
{
  "measures": ["orders.amount_usd"],
  "dimensions": ["orders.currency"],
  "timeDimensions": [
    {
      "dimension": "orders.created_at",
      "granularity": "day"
    }
  ]
}
```

## Result

Cube serves the query from `orders_with_fx_rollup`, joining the cached
`orders_rollup` (refreshed daily) with the cached `fx_rates_rollup`
(refreshed hourly). The heavy aggregation never rebuilds when FX rates
change, but the converted totals always reflect the latest rates.

```javascript
[
  {
    "orders.created_at.day": "2026-05-19T00:00:00.000",
    "orders.currency": "EUR",
    "orders.amount_usd": "12450.32"
  },
  {
    "orders.created_at.day": "2026-05-19T00:00:00.000",
    "orders.currency": "GBP",
    "orders.amount_usd": "8930.17"
  }
]
```
