Have you ever come across a situation where you needed to perform complex calculations or apply conditional logic on a column in your SQL Server database? If so, computed columns can be a powerful tool to help you achieve this. In this blog post, we will explore the concept of computed columns and how they can be used effectively in your SQL Server applications.

What are Computed Columns?

A computed column is a virtual column that is not physically stored in the database but is computed based on an expression or formula involving other columns in the same table. It allows you to define a column that automatically calculates its value based on the values of other columns.

Let’s take an example to understand this better. Suppose we have a table called “WorkOrder” in our database, which contains information about work orders and their quantities. We want to add a column that categorizes the order quantity based on certain conditions. For example, if the order quantity is less than 10, it should be categorized as “Single Digit”, if it is between 10 and 100, it should be categorized as “Double Digit”, and so on.

To achieve this, we can use a computed column with a CASE statement. Here’s an example:

-- Add Computed Column with Case Statement
ALTER TABLE [Production].[WorkOrder]
ADD OrderVol AS CAST
(
CASE
WHEN OrderQty < 10 THEN 'Single Digit'
WHEN OrderQty >= 10 AND OrderQty < 100 THEN 'Double Digit'
WHEN OrderQty >= 100 AND OrderQty < 1000 THEN 'Three Digit'
ELSE 'Super Large'
END AS VARCHAR(100)
)

Once the computed column is added, it will automatically calculate the category for each row based on the order quantity. You can then include this computed column in your SELECT statements to retrieve the categorized data.

Benefits of Computed Columns

Computed columns offer several benefits:

• Consistency: Computed columns ensure that the calculated values are always up-to-date and consistent, as they are automatically recalculated whenever the underlying data changes.
• Performance: By pre-calculating values and storing them in a computed column, you can improve query performance, as the calculations are done only once during data insertion or update, rather than every time the data is queried.
• Code Reusability: Once you have defined a computed column, you can reuse it in multiple queries without having to rewrite the calculation logic.

Conclusion

Computed columns are a powerful feature in SQL Server that allow you to perform complex calculations and apply conditional logic on your data. They provide consistency, improve performance, and promote code reusability. By understanding how to use computed columns effectively, you can enhance the functionality and efficiency of your SQL Server applications.

Do you have any thoughts or questions about computed columns? Feel free to leave a comment below. I would love to hear from you!