Unlocking the Power of BigQuery: How to Get SESSIONS with UNNEST Function?

Are you tired of struggling to extract insights from your Google BigQuery data? Do you find yourself lost in a sea of complex queries and confusing syntax? Fear not, dear data enthusiast, for today we’re going to dive into the fascinating world of BigQuery’s UNNEST function and explore how to harness its power to get SESSIONS from your data!

What is the UNNEST Function in BigQuery?

Before we dive into the juicy stuff, let’s take a step back and understand what the UNNEST function does. In simple terms, UNNEST is a table function that takes an array as input and returns a table with a single row for each element in the array. Think of it as a way to “unnest” or “explode” an array into individual rows.

When to Use UNNEST Function?

So, when should you use the UNNEST function in BigQuery? Well, my friend, this function shines in scenarios where you have an array of values and you want to perform operations on each individual element. Here are some common use cases:

• Converting JSON data into a tabular format
• Extracting individual values from an array column
• Performing aggregation operations on array elements
• Creating sessions from event-based data

Getting SESSIONS with UNNEST Function in BigQuery

Now that we’ve covered the basics, let’s get to the main event! Suppose you have a table with event-based data, and you want to create sessions based on a specific criteria. For example, let’s say you have a table called `events` with the following columns:

user_id	event_type	event_time
1	login	2022-01-01 10:00:00
1	browse	2022-01-01 10:05:00
1	purchase	2022-01-01 10:10:00
2	login	2022-01-01 11:00:00
2	browse	2022-01-01 11:05:00

In this example, we want to create sessions based on the user’s activity, where a session is defined as a sequence of events within a 30-minute window.

Step 1: Create an Array of Events for Each User

The first step is to create an array of events for each user. We can do this using the `ARRAY_AGG` function in BigQuery:

WITH events AS (
  SELECT user_id, event_type, event_time,
    ARRAY_AGG(event_time) OVER (PARTITION BY user_id ORDER BY event_time) AS event_array
  FROM events_table
)

This will create a new table with an array of event times for each user.

Step 2: Use UNNEST to Create Individual Rows for Each Event

Next, we’ll use the UNNEST function to create individual rows for each event in the array:

WITH events AS (
  SELECT user_id, event_type, event_time,
    ARRAY_AGG(event_time) OVER (PARTITION BY user_id ORDER BY event_time) AS event_array
  FROM events_table
),
unnested_events AS (
  SELECT user_id, event_type, event_time
  FROM events, UNNEST(event_array) AS event_time
)

This will create a new table with individual rows for each event.

Step 3: Create Sessions Using a 30-Minute Window

Now, we’ll use a window function to create sessions based on the 30-minute window:

WITH events AS (
  SELECT user_id, event_type, event_time,
    ARRAY_AGG(event_time) OVER (PARTITION BY user_id ORDER BY event_time) AS event_array
  FROM events_table
),
unnested_events AS (
  SELECT user_id, event_type, event_time
  FROM events, UNNEST(event_array) AS event_time
),
sessions AS (
  SELECT user_id, event_type, event_time,
    SESSION_NUMBER() OVER (PARTITION BY user_id ORDER BY event_time ROWS 30 MINUTES PRECEDING) AS session_id
  FROM unnested_events
)

This will create a new table with a `session_id` column that groups events within a 30-minute window.

Putting it All Together

Now that we’ve covered the individual steps, let’s put it all together in a single query:

WITH events AS (
  SELECT user_id, event_type, event_time,
    ARRAY_AGG(event_time) OVER (PARTITION BY user_id ORDER BY event_time) AS event_array
  FROM events_table
),
unnested_events AS (
  SELECT user_id, event_type, event_time
  FROM events, UNNEST(event_array) AS event_time
),
sessions AS (
  SELECT user_id, event_type, event_time,
    SESSION_NUMBER() OVER (PARTITION BY user_id ORDER BY event_time ROWS 30 MINUTES PRECEDING) AS session_id
  FROM unnested_events
)
SELECT *
FROM sessions;

This query will give you a table with individual rows for each event, grouped into sessions based on the 30-minute window.

Conclusion

In this article, we’ve explored the power of BigQuery’s UNNEST function and how to use it to get SESSIONS from event-based data. By following these steps, you can unlock new insights from your data and gain a deeper understanding of your users’ behavior.

Remember, the UNNEST function is a powerful tool in your BigQuery toolkit, and with practice, you’ll be able to tackle even the most complex data challenges.

So, what are you waiting for? Get started with BigQuery today and start unlocking the secrets of your data!

Happy querying!

Frequently Asked Question

Get ready to unleash the power of UNNEST function in Google BigQuery and master the art of getting SESSIONS!