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> Reference material for LAG function

# LAG OVER

Returns the value of the input expression at the given offset before the current row within the requested window.

For more information on usage, please refer to [Window Functions](/reference-sql/functions-reference/window).

## Syntax

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

## Parameters

| Parameter        | Description                                                                                                                                                                                                    | Supported input types |
| :--------------- | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | :-------------------- |
| `<expression>`   | Any valid expression that will be returned based on the `<offset>.`                                                                                                                                            | Any                   |
| `<offset>`       | The number of rows backward from the current row from which to obtain a value. A negative number will act as [LEAD()](/reference-sql/functions-reference/window/lead). The offset must be a literal `INTEGER`. | `INTEGER`             |
| `<default>`      | The expression to return when the offset goes out of the bounds of the window. Must be a literal of the same type as `<expression>`. The default is `NULL`.                                                    | Any                   |
| `<partition_by>` | The expression used for the `PARTITION BY` clause.                                                                                                                                                             | Any                   |
| `<order_by>`     | An expression used for the `ORDER BY` clause.                                                                                                                                                                  | Any                   |

## Example

In the example below, `LAG` returns the nickname of the player one position behind (`player_before`) and one position ahead (`player_after`) in alphabetical order within each level. `NULL` is returned when no row exists at the given offset.

<div className="query-window">
  ```
  SELECT
      nickname,
      level,
      LAG(nickname, 1) OVER (PARTITION BY level ORDER BY nickname) AS player_before,
      LAG(nickname, -1) OVER (PARTITION BY level ORDER BY nickname) AS player_after
  FROM
      (VALUES
          ('kennethpark', 9),
          ('rileyjon', 9),
          ('sabrina21', 9),
          ('ymatthews', 9)
      ) AS t(nickname, level);
  ```

  | nickname <span>text</span> | level <span>int</span> | player\_before <span>text null</span> | player\_after <span>text null</span> |
  | :------------------------- | :--------------------- | :------------------------------------ | :----------------------------------- |
  | kennethpark                | 9                      | NULL                                  | rileyjon                             |
  | rileyjon                   | 9                      | kennethpark                           | sabrina21                            |
  | sabrina21                  | 9                      | rileyjon                              | ymatthews                            |
  | ymatthews                  | 9                      | sabrina21                             | NULL                                 |

  <p><span>Rows: 4</span><span>Execution time: 6.89ms</span></p>
</div>