When working with datasets that contain information about tourist attractions, it is often necessary to find the first occurrence of each attraction. This can be achieved using the FIRST_VALUE function in SQL.

The FIRST_VALUE function allows you to retrieve the first value from an ordered set of rows based on a specified column. It is commonly used in scenarios where you want to find the earliest or first occurrence of a particular attribute.

To demonstrate how to use the FIRST_VALUE function, let’s assume we have a dataset called attractions with the following schema:

We want to find the first occurrence of each tourist attraction based on the date_visited column.

The SQL query to achieve this using FIRST_VALUE would look like this:

SELECT DISTINCT
  attraction_id,
  FIRST_VALUE(attraction_name) OVER (PARTITION BY attraction_name ORDER BY date_visited) AS first_occurrence,
  city,
  date_visited
FROM attractions;

Let’s break down the query:

• The FIRST_VALUE function is applied to the attraction_name column and ordered by date_visited within each partition of distinct attraction names.
• The PARTITION BY clause groups the dataset by the distinct values of attraction_name, creating partitions for each unique attraction.
• The ORDER BY clause sorts the rows within each partition based on the date_visited column in ascending order.
• The DISTINCT keyword ensures that each attraction appears only once in the result set.

The result of the above query would be:

By using the FIRST_VALUE function with the appropriate ordering, we were able to identify the first occurrence of each tourist attraction in the dataset.

[#SQL #DataAnalysis]