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Discover how to properly load Avro epoch datetime values into BigQuery as timestamps, ensuring accurate data representation.
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Converting Avro Epoch Datetime to BigQuery Timestamp: A Step-by-Step Guide

When working with data stored in Avro files, particularly in Google Cloud Storage (GCS), you may encounter challenges related to loading datetime values into BigQuery. One common issue arises when you have epoch time values stored as Long type fields. This guide will guide you on how to properly convert these epoch datetime values into the correct Timestamp format when loading data into BigQuery.

Understanding the Problem

In your Avro files, you might have fields that contain epoch time values represented as long integers. For example, a value like 1614004223589 represents a specific point in time—February 22, 2021, at 14:28:56 UTC. However, when you attempt to load this data into BigQuery with the Timestamp field type, you may end up with incorrect timestamps, such as 1970-01-19 16:20:04.135924 UTC. This discrepancy typically occurs because BigQuery expects timestamps in milliseconds or microseconds, while the original data might only be provided in seconds.

To solve this problem, let's break down the solution into clear, actionable steps.

Solution Overview

Step 1: Load Data in Original Format

Begin by loading your data to BigQuery in the same format as it is available in your source Avro files. This ensures that you have the raw data intact before applying any transformations. Here's how you can do it:

Create an empty BigQuery table with the appropriate schema, ensuring that the field containing epoch time is defined as a Long type.

Load your Avro file into this table using either the BigQuery command line tool or the BigQuery console.

Step 2: Create a View for Date Transformations

After successfully loading the data, the next step is to create a view that applies the necessary transformations to convert the epoch time values into the desired Timestamp format.

Create the View:

In BigQuery, create a view based on your loaded table.

Apply Date Transformations:

Use the TIMESTAMP_SECONDS function to convert the epoch timestamp. An example SQL query could look like this:

[[See Video to Reveal this Text or Code Snippet]]

Use the View for Future Queries:

Always query the view for data, ensuring you are using the transformed timestamp values.

Alternate Solution: Use a Transformed Function

If you want to simplify the process further, consider creating a custom function in BigQuery to handle the date transformations before calling the data.

Load Data as Before:

Again, load the data into BigQuery in its original format.

Create a Transformation Function:

Make a BigQuery function to handle the epoch conversion.

Here's an example definition of such a function:

[[See Video to Reveal this Text or Code Snippet]]

Apply Function When Querying:

Use the newly created function when you query your table:

[[See Video to Reveal this Text or Code Snippet]]

Final Thoughts

By following these steps, you can successfully convert epoch datetime values from Avro into the desired Timestamp format in BigQuery. Loading the data in its raw format allows for accurate transformations using views or custom functions, ensuring your analysis is based on correct time representations.

If you encounter issues or have questions during this process, feel free to reach out for further assistance! Happy querying!