Add example and usecase using Partition by (#5677)

* Add example using partition by

* Addressed admin feedback: Tables format and headers

* Update content/sql/concepts/window-functions/terms/lag/lag.md

* Fix formatting of SQL queries

* Update lag.md

* Update lag.md

* Update lag.md

* Update lag.md

* Update lag.md

* Update lag.md

* Fix lint errors

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content/sql/concepts/window-functions/terms/lag/lag.md

@@ -43,19 +43,63 @@ Users Table
 | kyle       | xy        | 60  |
 
 ```sql
-SELECT *,
+SELECT
+    first_name,
+    last_name,
+    age,
     LAG(age, 1) OVER (
-  ORDER BY age ASC) AS previous_age
+        ORDER BY age DESC
+    ) AS previous_age
 FROM Users;
 ```
 
-The output is a table that features a new column `previous_age`, which holds the values from the previous records. The first record is null because a default was not specified and the previous row would be out of range.
-
-Output
+The output of the above code is a table that features a new column `previous_age`, which holds the values from the previous records. The first record is null because a default was not specified and the previous row would be out of range.
 
 | first_name | last_name | age | previous_age |
 | ---------- | --------- | --- | ------------ |
-| kyle       | xy        | 60  | null         |
+| kyle       | xy        | 60  | NULL         |
 | jenna      | black     | 35  | 60           |
 | chris      | smith     | 30  | 35           |
 | dave       | james     | 19  | 30           |
+
+### Using `PARTITION BY` Clause
+
+This example demonstrates how to use the `LAG()` function to create a new column, `previous_position`.
+
+The `PARTITION BY employee_id` clause ensures that the `LAG()` function operates within each group of rows that share the same `employee_id`. The `ORDER BY promotion_date` ensures the rows are processed in chronological order.
+
+`Promotions` Table
+
+| employee_id | promotion_date | new_position |
+| ----------- | -------------- | ------------ |
+| 1           | 2020-01-01     | Junior Dev   |
+| 1           | 2021-06-01     | Mid Dev      |
+| 1           | 2024-03-01     | Senior Dev   |
+| 2           | 2019-05-01     | Intern       |
+| 2           | 2022-11-01     | Analyst      |
+| 2           | 2024-11-20     | Data Analyst |
+
+```sql
+SELECT
+    employee_id,
+    promotion_date,
+    new_position,
+    LAG(new_position) OVER (
+        PARTITION BY employee_id
+        ORDER BY promotion_date
+    ) AS previous_position
+FROM Promotions;
+```
+
+Within each group defined by `employee_id`, the `previous_position` column holds the value from the previous row based on `promotion_date`. The first record in each group is `NULL` because there is no preceding row.
+
+The above code generates the following output:
+
+| employee_id | promotion_date | new_position | previous_position |
+| ----------- | -------------- | ------------ | ----------------- |
+| 1           | 2020-01-01     | Junior Dev   | NULL              |
+| 1           | 2021-06-01     | Mid Dev      | Junior Dev        |
+| 1           | 2024-03-01     | Senior Dev   | Mid Dev           |
+| 2           | 2019-05-01     | Intern       | NULL              |
+| 2           | 2022-11-01     | Analyst      | Intern            |
+| 2           | 2024-11-20     | Data Analyst | Analyst           |