In SQL, FIRST_VALUE is a window function that allows you to perform calculations on the first value in a group of rows. It can be particularly useful when you want to calculate running totals, cumulative sums, or compare each row with the first row in a group.
The basic syntax of using FIRST_VALUE is as follows:
FIRST_VALUE(expression) OVER (PARTITION BY column ORDER BY column ASC/DESC)
Let’s take a look at an example to demonstrate how FIRST_VALUE works:
SELECT category, product, price,
FIRST_VALUE(price) OVER (PARTITION BY category ORDER BY price ASC) AS lowest_price
FROM products
In this example, we have a table called products that contains information about various products, including the category, product name, and price. We want to find the lowest price for each category.
By using FIRST_VALUE(price) OVER (PARTITION BY category ORDER BY price ASC), we calculate the lowest price for each group of products within the same category. The PARTITION BY clause divides the rows into groups based on the category column, and the ORDER BY clause sorts the rows within each group by price in ascending order.
The result will include the original columns (category, product, price) and an additional column called lowest_price, which displays the first value (lowest price) for each category.
Using FIRST_VALUE, you can also perform other calculations based on the first value, such as finding the highest value, calculating the difference between each row and the first row, or determining if a row is equal to the first row.
Keep in mind that FIRST_VALUE is just one of many window functions available in SQL. You can explore other functions like LAST_VALUE, LAG, and LEAD to perform various calculations and comparisons on different rows within a group.
Now that you understand how to use FIRST_VALUE in SQL, you can leverage this powerful function to perform calculations and analysis on the first value in your data sets.
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