# Distinct array aggregation

Use `array_agg(DISTINCT ...)` to collect unique admitted values into an array. An aggregate ORDER BY defines the resulting element order.

The CoordinatorDB function is array_agg; `groupArrayDistinct` is not a callable alias.

## Collect distinct values

```sql
CREATE TABLE labels (value INTEGER);
INSERT INTO labels VALUES (2), (1), (2), (NULL);
```

```sql
SELECT array_agg(DISTINCT value ORDER BY value NULLS LAST)
FROM labels
FORMAT csv;
```

```text
"[1,2,null]"
```

Array aggregation retains NULL as an element. DISTINCT keeps one copy of it.

## Exclude missing elements

Use FILTER when the result should contain only present values:

```sql
SELECT array_agg(DISTINCT value ORDER BY value)
       FILTER (WHERE value IS NOT NULL)
FROM labels
FORMAT csv;
```

```text
"[1,2]"
```

See [`array_agg`](https://coordinatordb.com/docs/reference/functions/aggregate-functions/array-agg) for empty input and element types, and [array functions](https://coordinatordb.com/docs/reference/functions/regular-functions/array-functions) for operations on the result.