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# uniqArray

> Example of using the uniqArray combinator

<h2 id="description">
  Description
</h2>

The [`Array`](/reference/functions/aggregate-functions/combinators#-array) combinator
can be applied to the [`uniq`](/reference/functions/aggregate-functions/uniq)
function to calculate the approximate number of unique elements across all arrays,
using the `uniqArray` aggregate combinator function.

The `uniqArray` function is useful when you need to count unique elements across
multiple arrays in a dataset. It's equivalent to using `uniq(arrayJoin())`, where
`arrayJoin` first flattens the arrays and then `uniq` counts the unique elements.

<h2 id="example-usage">
  Example usage
</h2>

In this example, we'll use a sample dataset of user interests across different
categories to demonstrate how `uniqArray` works. We'll compare it with
`uniq(arrayJoin())` to show the difference in counting unique elements.

```sql title="Query" theme={null}
CREATE TABLE user_interests
(
    user_id UInt32,
    interests Array(String)
) ENGINE = Memory;

INSERT INTO user_interests VALUES
    (1, ['reading', 'gaming', 'music']),
    (2, ['gaming', 'sports', 'music']),
    (3, ['reading', 'cooking']);

SELECT 
    uniqArray(interests) AS unique_interests_total,
    uniq(arrayJoin(interests)) AS unique_interests_arrayJoin
FROM user_interests;
```

The `uniqArray` function counts unique elements across all arrays combined, similar to `uniq(arrayJoin())`.
In this example:

* `uniqArray` returns 5 because there are 5 unique interests across all users: 'reading', 'gaming', 'music', 'sports', 'cooking'
* `uniq(arrayJoin())` also returns 5, showing that both functions count unique elements across all arrays

```response title="Response" theme={null}
   ┌─unique_interests_total─┬─unique_interests_arrayJoin─┐
1. │                      5 │                          5 │
   └────────────────────────┴────────────────────────────┘
```

<h2 id="see-also">
  See also
</h2>

* [`uniq`](/reference/functions/aggregate-functions/uniq)
* [`arrayJoin`](/reference/functions/regular-functions/array-join)
* [`Array combinator`](/reference/functions/aggregate-functions/combinators#-array)
* [`uniqCombined`](/reference/functions/aggregate-functions/uniqCombined)