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# PostgreSQL ROLLUP

**Summary**: in this tutorial, you will learn how to use the PostgreSQL `ROLLUP` to generate multiple grouping sets.

## Introduction to the PostgreSQL ROLLUP

The PostgreSQL `ROLLUP` is a subclause of the [`GROUP BY`](https://neon.com/postgresql/postgresql-tutorial/postgresql-group-by) clause that offers a shorthand for defining multiple [grouping sets](https://neon.com/postgresql/postgresql-tutorial/postgresql-grouping-sets). A grouping set is a set of columns by which you group. Check out the [grouping sets](https://neon.com/postgresql/postgresql-tutorial/postgresql-grouping-sets) tutorial for detailed information.

Different from the [`CUBE`](https://neon.com/postgresql/postgresql-tutorial/postgresql-cube) subclause, `ROLLUP` does not generate all possible grouping sets based on the specified columns. It just makes a subset of those.

The `ROLLUP` assumes a hierarchy among the input columns and generates all grouping sets that make sense considering the hierarchy. This is the reason why `ROLLUP` is often used to generate the subtotals and the grand total for reports.

For example, the `CUBE (c1,c2,c3)` makes all eight possible grouping sets:

```
(c1, c2, c3)
(c1, c2)
(c2, c3)
(c1,c3)
(c1)
(c2)
(c3)
()

```

However, the `ROLLUP(c1,c2,c3)` generates only four grouping sets, assuming the hierarchy `c1 > c2 > c3` as follows:

```
(c1, c2, c3)
(c1, c2)
(c1)
()

```

A common use of  `ROLLUP` is to calculate the aggregations of data by year, month, and date, considering the hierarchy `year > month > date`

The following illustrates the syntax of the PostgreSQL `ROLLUP`:

```sql
SELECT
    c1,
    c2,
    c3,
    aggregate(c4)
FROM
    table_name
GROUP BY
    ROLLUP (c1, c2, c3);

```

It is also possible to do a partial roll up to reduce the number of subtotals generated.

```sql
SELECT
    c1,
    c2,
    c3,
    aggregate(c4)
FROM
    table_name
GROUP BY
    c1,
    ROLLUP (c2, c3);

```

## PostgreSQL ROLLUP examples

If you haven't created the sales table, you can use the following script:

```sql
DROP TABLE IF EXISTS sales;
CREATE TABLE sales (
    brand VARCHAR NOT NULL,
    segment VARCHAR NOT NULL,
    quantity INT NOT NULL,
    PRIMARY KEY (brand, segment)
);

INSERT INTO sales (brand, segment, quantity)
VALUES
    ('ABC', 'Premium', 100),
    ('ABC', 'Basic', 200),
    ('XYZ', 'Premium', 100),
    ('XYZ', 'Basic', 300);

```

The following query uses the `ROLLUP` clause to find the number of products sold by brand (subtotal) and by all brands and segments (total).

```sql
SELECT
    brand,
    segment,
    SUM (quantity)
FROM
    sales
GROUP BY
    ROLLUP (brand, segment)
ORDER BY
    brand,
    segment;

```

![PostgreSQL ROLLUP example](https://neon.com/postgresqltutorial/PostgreSQL-ROLLUP-example.png)
As you can see clearly from the output, the third row shows the sales of the `ABC` brand, the sixth row displays sales of the `XYZ` brand. The last row shows the grand total for all brands and segments. In this example, the hierarchy is `brand > segment`.

If you change the order of brand and segment, the result will be different as follows:

```sql
SELECT
    segment,
    brand,
    SUM (quantity)
FROM
    sales
GROUP BY
    ROLLUP (segment, brand)
ORDER BY
    segment,
    brand;

```

![PostgreSQL ROLLUP example 2](https://neon.com/postgresqltutorial/PostgreSQL-ROLLUP-example-2.png)
In this case, the hierarchy is the `segment > brand`.

The following statement performs a partial roll-up:

```sql
SELECT
    segment,
    brand,
    SUM (quantity)
FROM
    sales
GROUP BY
    segment,
    ROLLUP (brand)
ORDER BY
    segment,
    brand;

```

![PostgreSQL ROLLUP - partial roll up](https://neon.com/postgresqltutorial/PostgreSQL-ROLLUP-partial-roll-up.png)
See the following `rental` table from the [sample database](../postgresql-getting-started/postgresql-sample-database).

![Rental Table](https://neon.com/postgresqltutorial/rental.png)
The following statement finds the number of rental per day, month, and year by using the `ROLLUP`:

```sql
SELECT
    EXTRACT (YEAR FROM rental_date) y,
    EXTRACT (MONTH FROM rental_date) M,
    EXTRACT (DAY FROM rental_date) d,
    COUNT (rental_id)
FROM
    rental
GROUP BY
    ROLLUP (
        EXTRACT (YEAR FROM rental_date),
        EXTRACT (MONTH FROM rental_date),
        EXTRACT (DAY FROM rental_date)
    );

```

![PostgreSQL ROLLUP example with year month and date](https://neon.com/postgresqltutorial/PostgreSQL-ROLLUP-example-with-year-month-and-date.png)
In this tutorial, you have learned how to use the PostgreSQL `ROLLUP` to generate multiple grouping sets.

---

## Related docs (Group Data)

- [GROUP BY](https://neon.com/postgresql/postgresql-tutorial/postgresql-group-by)
- [HAVING](https://neon.com/postgresql/postgresql-tutorial/postgresql-having)
- [GROUPING SETS](https://neon.com/postgresql/postgresql-tutorial/postgresql-grouping-sets)
- [CUBE](https://neon.com/postgresql/postgresql-tutorial/postgresql-cube)