# Work with arrays

Arrays retain an ordered collection with one member type. Use explicit declarations when the element range or nullability must be enforced.

## Create and read an array

```sql
SELECT array_element(array(10, 20, 30), -1),
       array_length(array(10, 20, 30))
FORMAT csv;
```

```text
30,3
```

Element positions are one-based; negative positions count from the end. Zero is invalid. A missing position returns the declared member type's default. This differs from array_position, which returns NULL when a value is not found.

## Expand into rows

Use unnest in FROM to expand the scalar leaves:

```sql
SELECT unnest AS value
FROM unnest(array(10, 20, 30))
ORDER BY unnest
FORMAT csv;
```

```text
10
20
30
```

## Collect rows

Array aggregation can restore an ordered collection and retain missing elements:

```sql
CREATE TABLE readings (value INTEGER);
INSERT INTO readings VALUES (20), (10), (NULL);
```

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

```text
"[10,20,null]"
```

Use Array(Nullable(T)) when typed input must admit NULL members. Bracket access and lambda expressions are not supported; use the documented functions.

See [Array](https://coordinatordb.com/docs/reference/data-types/array), [array functions](https://coordinatordb.com/docs/reference/functions/regular-functions/array-functions) and [`array_agg`](https://coordinatordb.com/docs/reference/functions/aggregate-functions/array-agg).