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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":"github-light","dark":"github-dark"}}
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, the `LAG` function is being used to find the players in each level who ranked before and after a certain player. In some cases, if the player has no one ranked before or after them, the `LAG` function returns `NULL`.

```sql theme={"theme":{"light":"github-light","dark":"github-dark"}}
SELECT
	nickname,
	level,
	LAG(nickname, 1) OVER (PARTITION BY level ORDER BY nickname) AS player_before,
	LAG(first_name, -1) OVER (PARTITION BY level ORDER BY nickname) AS player_after
FROM
	players;
```

**Returns**:

| nickname    | level | player\_before | player\_after |
| :---------- | :---- | :------------- | :------------ |
| kennethpark | 9     | NULL           | rileyjon      |
| rileyjon    | 9     | kennethpark    | sabrina21     |
| sabrina21   | 9     | rileyjon       | ymatthews     |
| ymatthews   | 9     | sabrina21      | NULL          |