# Source: https://docs.oxla.com/sql-reference/sql-functions/window-functions/first-value.md

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# FIRST_VALUE()

## Overview

The `FIRST_VALUE()` is a window function that retrieves the first value in an ordered set of values within a specified partition.

## Syntax

The syntax for this function is as follows:

```sql  theme={null}
FIRST_VALUE(expression) OVER (
    [PARTITION BY partition_expression]
    ORDER BY sort_expression
    RANGE BETWEEN start_value AND end_value
)
```

## Parameters

* `expression`: target column or expression that the function operates on
* `PARTITION BY`: optional clause, which divides the result set into partitions to which the `FIRST_VALUE()` function is applied (if omitted, the entire result set is treated as a single partition)
* `ORDER BY`: order of rows in each partition to which the function is applied
* `RANGE BETWEEN`: range-based window frame relative to the current row

## Example

For the needs of this section, we will use a simplified version of the `film` table from the Pagila database, containing only the `title`, `length` and `rating` columns. The complete schema for the `film` table can be found on the
<a href="https://www.postgresql.org/ftp/projects/pgFoundry/dbsamples/pagila/pagila/" target="_blank">Pagila</a> database website.

```sql  theme={null}
DROP TABLE IF EXISTS film;
CREATE TABLE film (
  title text NOT NULL,
  length int,
  rating text
);
INSERT INTO film(title, length, rating) VALUES
  ('ATTRACTION NEWTON', 83, 'PG-13'),
  ('CHRISTMAS MOONSHINE', 150, 'NC-17'),
  ('DANGEROUS UPTOWN', 121, 'PG'),
  ('KILL BROTHERHOOD', 54, 'G'),
  ('HALLOWEEN NUTS', 47, 'PG-13'),
  ('HOURS RAGE', 122, 'NC-17'),
  ('PIANIST OUTFIELD', 136, 'NC-17'),
  ('PICKUP DRIVING', 77, 'G'),
  ('INDEPENDENCE HOTEL', 157, 'NC-17'),
  ('PRIVATE DROP', 106, 'PG'),
  ('SAINTS BRIDE', 125, 'G'),
  ('FOREVER CANDIDATE', 131, 'NC-17'),
  ('MILLION ACE', 142, 'PG-13'),
  ('SLEEPY JAPANESE', 137, 'PG'),
  ('WRATH MILE', 176, 'NC-17'),
  ('YOUTH KICK', 179, 'NC-17'),
  ('CLOCKWORK PARADISE', 143, 'PG-13');
```

The query below uses the `FIRST_VALUE()` function to retrieve the title of the film with the shortest duration, partitioning results by rating and ordering by length.

```sql  theme={null}
SELECT
  title,
  length,
  rating,
  FIRST_VALUE(title) OVER (
    PARTITION BY rating
    ORDER BY
      length ASC ROWS BETWEEN UNBOUNDED PRECEDING
      AND UNBOUNDED FOLLOWING
  ) AS shortest_film_in_rating
FROM film;
```

By executing the code above, we will get the following output:

```bash  theme={null}
|   title             |   length   |   rating   |   shortest_film_in_rating   | 
|---------------------|------------|------------|-----------------------------|
| KILL BROTHERHOOD    | 54         | G          | KILL BROTHERHOOD            |
| PICKUP DRIVING      | 77         | G          | KILL BROTHERHOOD            |
| SAINTS BRIDE        | 125        | G          | KILL BROTHERHOOD            |
| HOURS RAGE          | 122        | NC-17      | HOURS RAGE                  |
| FOREVER CANDIDATE   | 131        | NC-17      | HOURS RAGE                  | 
| PIANIST OUTFIELD    | 136        | NC-17      | HOURS RAGE                  |
| CHRISTMAS MOONSHINE | 150        | NC-17      | HOURS RAGE                  |
| INDEPENDENCE HOTEL  | 157        | NC-17      | HOURS RAGE                  |
| WRATH MILE          | 176        | NC-17      | HOURS RAGE                  |
| YOUTH KICK          | 179        | NC-17      | HOURS RAGE                  |
| PRIVATE DROP        | 106        | PG         | PRIVATE DROP                |  
| DANGEROUS UPTOWN    | 121        | PG         | PRIVATE DROP                |     
| SLEEPY JAPANESE     | 137        | PG         | PRIVATE DROP                |      
| HALLOWEEN NUTS      | 47         | PG-13      | HALLOWEEN NUTS              |      
| ATTRACTION NEWTON   | 83         | PG-13      | HALLOWEEN NUTS              |     
| MILLION ACE         | 142        | PG-13      | HALLOWEEN NUTS              |     
| CLOCKWORK PARADISE  | 143        | PG-13      | HALLOWEEN NUTS              |          
```