Using FIRST_VALUE to find the first occurrence of a phone number in a dataset

20 Oct 2023

In data analysis and processing, it is often necessary to find the first occurrence of a specific value in a dataset. This becomes especially relevant when dealing with large datasets where identifying the first occurrence of a particular value is crucial. One common scenario is finding the first occurrence of a phone number in a dataset.

In SQL, you can use the FIRST_VALUE function to accomplish this task. FIRST_VALUE is an analytical function that returns the first value in an ordered set of values.

Syntax

The syntax for using FIRST_VALUE is as follows:

FIRST_VALUE(expression) OVER (
    [PARTITION BY partition_expression]
    ORDER BY sort_expression
    ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
) 

The key components of this syntax are:

expression: The value you want to retrieve the first occurrence of.
PARTITION BY: (Optional) If you want to partition the dataset by a specific column before finding the first value, you can specify it here.
ORDER BY: The column you want to order the dataset by in order to determine the first value.
ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW: This specifies the range of rows to consider when determining the first value.

Example

Let’s say we have a dataset named contacts with the following columns: contact_id, name, and phone_number.

contact_id	name	phone_number
1	John Doe	123-456-7890
2	Jane Smith	555-123-4567
3	Alex Johnson	987-654-3210
4	Sarah Adams	555-789-1234

To find the first occurrence of a phone number in this dataset, we can use the following SQL query:

SELECT DISTINCT
    FIRST_VALUE(phone_number) OVER (
        ORDER BY contact_id
        ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
    ) AS first_phone_number
FROM
    contacts;

This query will return the result:

first_phone_number
123-456-7890
123-456-7890
123-456-7890
123-456-7890

In this example, we use FIRST_VALUE to find the first occurrence of the phone_number column. The dataset is ordered by the contact_id column, ensuring that the first phone number is retrieved for each row.

Conclusion

Using FIRST_VALUE in SQL allows us to easily find the first occurrence of a specific value in a dataset. In the case of finding the first occurrence of a phone number, this function is particularly useful. By utilizing the ORDER BY clause, we can determine the first value based on a specific column. This can be a valuable tool for data analysis and processing tasks.