Understanding DATEDIFF() in BigQuery/Periscope

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When working with time-series data, particularly in the context of BigQuery or Periscope, it’s common to encounter date-based calculations. One such calculation is finding the difference between two dates, which can be a straightforward task when the dates are static. However, when dealing with dynamic or changing dates, things can get more complicated.

In this article, we’ll explore how to use DATEDIFF() for dynamically changing dates in BigQuery/Periscope. We’ll delve into the functions and syntax required to achieve this, along with some practical examples and explanations to help you master this skill.

Understanding Timestamp Diff

The first step in addressing dynamic date calculations is understanding the different types of timestamp data available in BigQuery. Periscope primarily uses timestamps for its data, which can be either Unix timestamps (the number of seconds since January 1, 1970) or integer values representing the number of milliseconds since the epoch.

When working with these timestamps, it’s essential to recognize that they represent a single point in time, rather than a date range. To calculate the difference between two dates, we need to use functions that can handle this type of data.

DATEDIFF() Function

In BigQuery, the DATEDIFF() function allows you to compute the difference between two timestamps or dates. However, as mentioned earlier, it’s crucial to choose the correct syntax for your specific use case.

When using DATEDIFF() with timestamps, we need to specify the unit of measurement. The default unit is days, but you can also use seconds or milliseconds by specifying the corresponding suffixes (e.g., DAYS, SECONDS, or MILLIS).

Let’s look at an example that demonstrates how to use DATEDIFF() with timestamps:

SELECT timestamp_diff(notification_ts, created_ts, DAY)

In this example, notification_ts and created_ts are the two timestamps for which we want to calculate the difference. The DAY suffix indicates that we’re working with days as the unit of measurement.

Using DATEDIFF() with Dates

When working with dates, things become slightly more complicated. BigQuery uses a specific format for date values: YYYY-MM-DD. To use DATEDIFF() with dates, we need to cast our date values to the correct data type (either DATE or TIMESTAMP).

Let’s look at an example that demonstrates how to use DATEDIFF() with dates:

SELECT DATE_DIFF(created_date, notification_date, DAY)

In this example, created_date and notification_date are the two date values for which we want to calculate the difference. The DAY suffix indicates that we’re working with days as the unit of measurement.

Handling Interval Calculations

When calculating intervals (e.g., 30 days before or after a notification), we need to use the DATE_ADD() and DATE_SUB() functions, respectively.

Here’s an example that demonstrates how to calculate the interval:

SELECT * FROM (
    SELECT notification_ts,
           created_ts,
           DATE_SUB(CAST(created_ts AS date), INTERVAL 30 DAY) AS previous_date,
           DATE_ADD(CAST(created_ts AS date), INTERVAL 30 DAY) AS next_date
    FROM notifications
)

In this example, we’re selecting all rows from the notifications table and using the DATE_SUB() and DATE_ADD() functions to calculate the previous and next dates.

Best Practices for Dynamic Date Calculations

When working with dynamic date calculations, it’s essential to follow best practices to ensure accuracy and consistency. Here are a few tips to keep in mind:

• Always specify the unit of measurement when using DATEDIFF() (e.g., DAYS, SECONDS, or MILLIS).
• Use the correct data type for date values (either DATE or TIMESTAMP).
• Verify that your calculations are accurate and consistent by testing them on sample data.
• Consider using interval calculations to handle complex scenarios, such as calculating the difference between two dates with time components.

Conclusion

Calculating the difference between dynamic dates in BigQuery/Periscope can be a challenging task, but it’s definitely achievable. By understanding how to use DATEDIFF() and other timestamp functions, you can create accurate and consistent date-based calculations that meet your specific requirements.

Remember to always specify the unit of measurement, use the correct data type for date values, verify your calculations, and consider using interval calculations when working with complex scenarios. With practice and experience, you’ll become proficient in handling dynamic date calculations, allowing you to unlock even more insights from your data.

Last modified on 2023-08-08