Скачать или смотреть How to Sum 3 Columns in SQL Using Conditional Logic

Learn how to efficiently sum values of different types in SQL with conditional logic to manage your business data effectively.
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This video is based on the question https://stackoverflow.com/q/76971220/ asked by the user 'José Erildo' ( https://stackoverflow.com/u/22442425/ ) and on the answer https://stackoverflow.com/a/76971437/ provided by the user 'Erik Blomgren' ( https://stackoverflow.com/u/2769378/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding How to Sum 3 Columns in SQL

When working with SQL databases, you might encounter situations where you need to sum values based on different criteria. For instance, you may have a table storing transaction values categorized by different types of services, such as 'Business', 'Enterprise', and 'Basic'. This post will guide you through the steps to sum values from these three columns effectively using SQL.

The Problem

Imagine you have a dataset, and you want to calculate the total sales for three specific types of services:

Business

Enterprise

Basic

The challenge here is to sum the values conditionally based on the type. Using your traditional SQL techniques, this might not be straightforward unless you understand how to structure your query effectively.

Expected Result

You would like the results to look something like this:

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

However, many users face issues with creating multiple Common Table Expressions (CTEs) that, when joined, produce conflicting results. So, let's explore a streamlined solution!

The Solution: Using CASE WHEN

One of the most reliable ways to sum your values based on different conditions is to use the CASE WHEN clause in your SQL query. This method allows you to evaluate each record's type and sum the values accordingly.

SQL Query Structure

Here’s how you can do it:

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

Breakdown of the Query

Select Statement: The SELECT clause is used to specify the data you want to retrieve. In this case, we are summing up the values.

CASE WHEN:

This clause checks the condition for Type.

If the type matches 'Business', it increments the sum by the value; if not, it returns NULL.

Sum Function: The SUM() function aggregates all the values returned by the CASE WHEN conditions.

From Clause: This specifies the table from which to pull the data.

Where Clause: It narrows down the records to those that match our specified types: 'Business', 'Enterprise', and 'Basic'.

Conclusion

By structuring your SQL query with CASE WHEN, you can efficiently sum the values based on multiple conditions without the hassle of multiple joins or CTEs that can complicate the outcome. This method not only simplifies your code but also enhances clarity and maintainability.

Feel free to implement this technique in your database queries, and you’ll find it smoother to handle conditional summation!