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> Reference material for FIRST_VALUE function

# FIRST_VALUE

Returns the first value evaluated in the specified window frame. If there are no rows in the window frame, returns NULL.

## Syntax

```sql theme={"theme":{"light":"github-light","dark":"github-dark"}}
FIRST_VALUE( <expression> ) OVER ( [ PARTITION BY <partition_by> ] ORDER BY <order_by> [ASC|DESC] )
```

## Parameters

| Parameter        | Description                                       | Supported input types |
| :--------------- | :------------------------------------------------ | :-------------------- |
| `<expression>`   | A SQL expression of any type to evaluate.         | Any                   |
| `<partition_by>` | An expression used for the `PARTITION BY` clause. | Any                   |
| `<order_by>`     | An expression used for the order by clause.       | Any                   |

## Return Types

Same as the input type of `<expression>`.

This function respects `NULL` values, and the results will be ordered with the default `NULL` ordering `NULLS LAST` unless

otherwise specified in the `ORDER BY` clause. If no `ORDER BY` clause is applied, the order will be undefined.

## Examples

The following code example selects the `nickname`, `level`, `current_score`, and `highest_score` for each level, using the `NTH_VALUE` function to retrieve the top score within each level, ordered by `current_score` in descending order.

**Example**

The following query uses `UNNEST` to convert an array `[1,2,5]` into a column, order the values, and returns the first value as `result`:

```sql theme={"theme":{"light":"github-light","dark":"github-dark"}}
SELECT FIRST_VALUE(a) OVER (ORDER BY a) as result FROM UNNEST(array[1,2,5]) as a;
```

**Returns**

| result (INTEGER) |
| :--------------- |
| 1                |
| 1                |
| 1                |

The previous code example returns the first element after ordering.

**Example**

The following query uses `UNNEST` to convert an array `[100, NULL, 1]` into a column, order the values, and returns the first value as `result`:

```sql theme={"theme":{"light":"github-light","dark":"github-dark"}}
SELECT FIRST_VALUE(a) OVER (ORDER BY a desc nulls first) as result FROM UNNEST(array[100,NULL,1]) as a;
```

**Returns**

| result (INTEGER) |
| :--------------- |
| NULL             |
| NULL             |
| NULL             |

The previous code example returns `NULL` values because `ORDER BY` specifies 'nulls first'.