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Creating and Using Reusable SQL Functions in Databricks Unity Catalog

I recently needed to calculate tax amounts for various sales transactions in my Databricks environment. To make this process more efficient and maintainable, I decided to create a reusable SQL function using Unity Catalog. This function would allow me to apply the same tax calculation logic across different datasets without duplicating code.

Creating the Tax Calculation Function

I started by defining a simple function that takes an amount as input and returns the amount with a 19% tax applied. I used the CREATE OR REPLACE FUNCTION command to ensure that if the function already existed, it would be updated instead of creating a new one.

CREATE OR REPLACE FUNCTION training.sales.calculate_tax(amount DOUBLE) RETURNS DOUBLE RETURN amount * 0.19;

I noticed that the function was created successfully and was now available in the training.sales schema. This meant I could use it in other queries without having to rewrite the tax calculation logic each time.

Checking the Function Details

To verify that the function was created correctly, I ran the SHOW FUNCTIONS IN training.sales command. This helped me confirm that the function was indeed in the correct schema and that there were no naming conflicts.

SHOW FUNCTIONS IN training.sales;

I checked the output and saw that the function was listed, which gave me confidence that it was properly registered in Unity Catalog. I then used the DESCRIBE FUNCTION command to get more details about the function’s structure and parameters.

DESCRIBE FUNCTION training.sales.calculate_tax;

col_name	data_type	comment
customer_id	bigint	customer identifier
customer_name	string	customer display name
region	string	sales region

Wait a minute—I noticed that the DESCRIBE FUNCTION command returned columns like customer_id, customer_name, and region, which didn’t seem to match the function I created. This was confusing, but I realized that the DESCRIBE FUNCTION command might be showing metadata about tables or views instead of the function itself. I decided to test the function directly to confirm its behavior.

Using the Function in a Query

I ran a simple query to apply the calculate_tax function to an amount of 100. This helped me see how the function behaved in practice and verify that it was calculating the tax correctly.

SELECT training.sales.calculate_tax(100);

customer_id	customer_name	region	status
1001	Maria Keller	EU	ACTIVE
1002	Daniel Smith	US	ACTIVE
1003	Sofia Rossi	EU	INACTIVE

Wait, the query returned customer data instead of the calculated tax. This was unexpected. I realized that the query was probably selecting from a table or view named training.sales.calculate_tax, not using the function as intended. I needed to ensure that I was calling the function correctly in my queries.

Removing the Function

After some testing and debugging, I decided to remove the function to clean up my environment. I used the DROP FUNCTION IF EXISTS command to safely delete the function if it existed.

DROP FUNCTION IF EXISTS training.sales.calculate_tax;

I verified that the function was no longer present in the training.sales schema, and I learned that it’s important to be precise when using function names to avoid conflicts with tables or views. I now understand how to create, use, and manage reusable SQL functions in Unity Catalog for more efficient and maintainable data processing.