How to Convert a String to a Date in BigQuery

Learn how to convert strings to dates in BigQuery effectively, ensuring your data transformation is accurate and efficient when dealing with date formats.
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Converting Strings to Dates in BigQuery: A Comprehensive Guide

When working with data in BigQuery, you may encounter scenarios where date values are stored in string format. This can lead to complications if you need to perform date operations or analyses. This guide addresses a common situation: how to convert a string representing a date into an actual date format in BigQuery while validating the data at the same time.

The Problem

Let's consider this example. You have a dataset with a column called follow_up_date that contains dates in string format. Your objective is to:

Validate whether entries in the follow_up_date column have the correct date format.

Replace invalid entries with the string "Not Set".

Convert the valid string dates into date format, allowing for better manipulation and analysis.

Implementing this requires handling and transforming the data appropriately, as simply filtering the strings won't give you date values directly. Below, we will explore a solution using BigQuery SQL syntax.

Step-by-Step Solution

Step 1: Validate the Date Format

First, you will use regular expressions to check if the strings in follow_up_date match a valid date format, such as MM-DD-YYYY or MM/DD/YYYY. If the format is valid, you keep the original date; if not, you return a default value "Not Set".

Here’s how you can implement this in SQL:

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

Step 2: Filter and Convert Valid Dates

Next, you want to filter out the rows where follow_up_date_mod is not "Not Set". In this step, you can also use the PARSE_DATE function to convert the valid strings into date values. Here’s how you can achieve this:

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

Step 3: Final Selection

Now that you have effectively converted the valid date strings to date format and filtered out the invalid entries, you can select the results for further analysis or reporting. The final query pulls together everything you need.

Conclusion

By implementing the above steps, you can efficiently handle strings that represent dates in BigQuery and convert them into a usable date format. This will streamline your data processing tasks and ensure your analyses are grounded in accurate and meaningful data.

Make sure to adapt the regex and date parsing format according to your specific date patterns when using this method. Happy querying!