Converting Date to Unix Timestamp in PostgreSQL

Details

Description

Learn how to change a PostgreSQL column from `date` to `int` to store Unix timestamps, along with a precise solution to avoid casting errors.
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This video is based on the question https://stackoverflow.com/q/65517313/ asked by the user 'Martin' ( https://stackoverflow.com/u/6365949/ ) and on the answer https://stackoverflow.com/a/65517711/ provided by the user 'Akhilesh Mishra' ( https://stackoverflow.com/u/7772483/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Converting Date to Unix Timestamp in PostgreSQL: A Step-by-Step Guide

When working with PostgreSQL, developers often face challenges in data type conversions. One such common scenario arises when you need to change a column's data type from date to int in order to store Unix timestamps. This guide addresses a common issue encountered during this process and provides a clear solution.

The Problem

Suppose you have a table named matches with a column called deleted_date of type date, which might contain values like 2020-12-30. You want to convert this deleted_date column to an int type, so that you can store Unix timestamps instead. The problem arises when you execute the following command:

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

However, this results in an error message:

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This error indicates that PostgreSQL does not support direct casting from the date type to integer. So, how can you successfully convert the deleted_date from a date to a Unix timestamp stored as an integer? Let's take a look at the solution!

The Solution

To solve this problem, we need to extract the Unix timestamp from the date column using the extract function along with epoch. Here’s how you can do it step-by-step:

Step 1: Use the ALTER TABLE Statement

You will need to execute the following SQL command to change the column type correctly:

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

Step 2: Explanation of the Command

ALTER TABLE matches: This part specifies which table you're modifying.

ALTER COLUMN deleted_date TYPE INT: This indicates that you want to change the type of the deleted_date column to int.

USING extract(epoch from deleted_date)::INT: This crucial part converts the deleted_date values from date to the Unix timestamp format (number of seconds since January 1, 1970). The extract(epoch from ...) function fetches the epoch time, and the ::INT casts it to an integer type.

Step 3: Run the Command

Once you've input the command as detailed above, execute it in your PostgreSQL database environment. This should complete the conversion successfully without any errors.

Conclusion

Changing the type of a date column to store Unix timestamps can be a bit tricky due to PostgreSQL's strict type casting rules. However, by using the extract function combined with epoch, you can seamlessly transition your data from a date format into a Unix timestamp format stored as an integer.

If you run into any issues or errors along the way, remember to double-check your syntax and ensure that your database structure supports the changes you are trying to make. Happy querying!