Скачать или смотреть How to Add a New Column to Your SQL Query Output with Conditional Logic

Learn how to enhance your SQL queries by adding a new column based on specific conditions, ensuring your data output meets your needs.
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This video is based on the question https://stackoverflow.com/q/62969836/ asked by the user 'prudhvi bikumalla' ( https://stackoverflow.com/u/11732416/ ) and on the answer https://stackoverflow.com/a/62969895/ provided by the user 'The Impaler' ( https://stackoverflow.com/u/6436191/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving SQL Query Challenges: Adding Conditional Columns

In the world of SQL, crafting the right query can sometimes feel like trying to find a needle in a haystack, especially when you're working to filter and display data according to specific conditions. One common challenge arises when you want to add a new column to your query output that derives its value based on certain conditions. If you're facing this issue, you've come to the right place!

The Challenge: Adding a New Column in the Output

Let's break down a scenario. You have a table called demo with the following columns:

FirstName

LastName

ReportsTo

Position

Age

Now you need to create a query that does two things:

Returns records where the ReportsTo field is either "JennyRichards" or null, and sorts these records by Age.

Adds a new column called BossTitle, which should display "CEO" if ReportsTo is "JennyRichards", otherwise, this column should be null.

But when you tried writing your SQL query, you encountered a syntax error. Let’s explore how to solve this problem effectively!

Crafting the Solution: The Correct SQL Query

Understanding the Error

The error in your initial query arises from incorrect syntax when defining the new column with a subquery. Instead, we should use a CASE statement for conditional logic. The CASE statement allows you to define when certain values should be displayed based on conditions you set.

Here’s the Correct Query to Use:

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

Breakdown of the Query

SELECT Clause: We're selecting the necessary columns (FirstName, LastName, etc.) along with our newly constructed BossTitle.

CASE Statement:

WHEN ReportsTo = 'JennyRichards' THEN 'CEO': This checks if the value of ReportsTo is "JennyRichards". If it is, it assigns 'CEO' to the new BossTitle column.

ELSE NULL: If ReportsTo isn't "JennyRichards", it assigns NULL to BossTitle. This ensures you have a clean representation of who is being reported to.

FROM Clause: Pulling records from the demo table.

WHERE Clause: Filtering the results to include records where ReportsTo is either "JennyRichards" or null.

ORDER BY Clause: Sorting the final output by the Age column in ascending order, as required.

Final Thoughts

With this solution, you can efficiently add a column based on conditions without running into syntax errors. By leveraging the power of the CASE statement, you gain flexibility in how your data is represented. This not only makes your SQL queries more dynamic but also enhances the clarity of your reports or outputs.

By following these guidelines, you should easily navigate the complexities of SQL queries and produce the exact output you need for your data requirements. Happy querying!