Sql User Defined Function Within Select

A deeper dive: optimizing UDF usage in a SELECT statement

How to test your UDF

As the SQL version of a "try before you buy" policy, testing your UDF standalone can safeguard against logic errors or data type mismatches:

-- Check if discount function gives an "employee discount" or more like a "meh" discount
SELECT dbo.GetDiscount(100) AS TestDiscountResult;
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Make aliases your best friend

You can simplify your script and increase its readability by assigning aliases to your UDFs:

-- Using alias because no one wants gibberish in their results, right?
SELECT ProductID, dbo.GetDiscount(Price) AS DiscountedPrice
FROM Products;
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Always validate the parameters and return type of your UDF

To prevent unanticipated behaviour and avoid potential outages, validate your parameters and return type. This will save you from scratching your heads over obscure null or incorrect results.

Error handling is a must in UDFs

Proactively incorporate error handling within your UDF to manage unexpected situations. This can be as simple as adding a TRY/CATCH block or using IF/ELSE conditions to make your function more robust.

The WHERE clause: not just for filtering anymore

Make your SQL queries more efficient by using a WHERE clause to filter results.

-- Excluding NULL ShipDates because who ships null dates anyway?
SELECT ProductID, dbo.GetBusinessDays(OrderDate, ShipDate) AS BusinessDaysToShip
FROM Orders
WHERE ShipDate IS NOT NULL;
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UDF authorization and definition: the unsung heroes

Is your UDF returning errors? Make sure you've granted the proper permissions for the user and correctly defined your functions. Else, you might be the star of a "you shall not pass" meme!

Scalar or Table-Valued? Choose your UDF wisely

If you need a single value, go for a scalar-valued UDF. If it's a whole set of results you're after, table-valued UDF is your go-to. Remember, SELECT clauses prefer scalar UDFs for their speed and efficiency.

An example to demonstrate business days calculation using a UDF

Don't know how many business days it took for a product to be delivered? Use a UDF to calculate it:

-- Time to find out if our shipping is faster than a turtle!
SELECT OrderID, dbo.GetBusinessDays(OrderDate, DeliveryDate) AS BusinessDays
FROM Orders;
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Check if your function GetBusinessDays tacitly counts holidays and weekends. Else, you might end up like Garfield, hating Mondays more than usual!

Visualization

Taking on a UDF in SQL is like stepping into a high-tech workshop. Armed with your 🛠️ custom tools, you transform raw data 🗂️ into valuable insights 🖼️:

SELECT 🛠️(Column1), Column2 FROM YourWorkshop;

Wouldn't it be great to fine-tune your data right within the SELECT statement itself, just like a master craftsman at his workbench? 🎨🛠️

Efficient and precise data transformations

Harness the power of UDFs to provide precise control over data manipulation, achieving an unmatched level of granularity and enhancing the readability of your query results.

Mastering the art of query performance

When it comes to SQL performance, every little bit counts. Consider the execution cost of your UDFs, optimize their complexity and reduce execution frequency for blazing-fast query speeds. Remember, a sleek SQL query is both an art🎨 and a science🔬!