In SQL, there are various window functions that allow us to perform calculations on a specific set of rows within a result set. One such function is FIRST_VALUE, which can be used to retrieve the first value of a specific column within a partitioned dataset.

Let’s say we have a table called products with the following structure:

If we want to find the first occurrence of each product name, we can use the FIRST_VALUE function along with the OVER clause. Here’s an example query:

SELECT DISTINCT name, 
       FIRST_VALUE(id) OVER (PARTITION BY name ORDER BY id) AS first_occurrence_id,
       FIRST_VALUE(price) OVER (PARTITION BY name ORDER BY id) AS first_occurrence_price
FROM products;

Here, we select distinct product names and use FIRST_VALUE to retrieve the first occurrence of the id and price columns for each product name. We partition the dataset by the name column and order the rows by id in ascending order.

The result of the above query will be:

In this result, we can see the first occurrence of each product name along with the corresponding id and price values.

Using FIRST_VALUE in this way can be useful when dealing with datasets where the order of occurrences matters, and you need to perform calculations or comparisons based on the first occurrence of a specific column.

In conclusion, the FIRST_VALUE function in SQL provides a simple and efficient way to find the first occurrence of a product name in a dataset while retaining the necessary contextual information. By utilizing the OVER clause and appropriate partitioning and ordering, you can retrieve the desired results.