Скачать или смотреть How to Resolve SQL Server Update Issues with Nested Case Statements

Discover how to fix the problem of SQL Server not updating records when using nested case statements and ensure your queries run smoothly.
---
This video is based on the question https://stackoverflow.com/q/65577131/ asked by the user 'saba' ( https://stackoverflow.com/u/14328778/ ) and on the answer https://stackoverflow.com/a/65577160/ provided by the user 'Sergey' ( https://stackoverflow.com/u/14535517/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Sql server not updating records with nested case statement in a query

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Resolving SQL Server Update Issues with Nested Case Statements

Using SQL Server for data manipulation is common, yet there are certain problems that can arise, particularly when updating records with complex queries. A common issue involves using nested case statements, which may lead to no records being updated despite seemingly correct SQL logic. If you've encountered this issue, you're not alone! In this guide, we'll explore why this happens and how to ensure your queries execute correctly.

The Problem at Hand

You may find yourself in a situation where running an update query with a nested case statement results in 0 row(s) affected. For example, you might have a query similar to the following:

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

What Went Wrong?

The primary issue in this query lies in the condition specified in the WHERE clause: WHERE column11 = NULL. In SQL, using the = operator to check for null values does not work as intended. Instead, the correct approach is to use the IS NULL or IS NOT NULL condition to evaluate null values effectively.

The Solution: Correcting the NULL Condition

Proper Syntax for NULL Checks

When you want to check if a column is null, you must modify the condition in your WHERE clause as follows:

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

This change will ensure that the SQL Server correctly identifies rows where column11 is null, allowing the update statement to execute properly.

Implementation Example

Here’s how your revised update query should look:

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

Why This Matters

Making sure to use IS NULL is not just a matter of syntax; it affects the logic and execution of your SQL queries significantly. The main points to keep in mind are:

NULL Handling: Always use IS NULL to check for null values.

Debugging: If your query is not updating records, check your WHERE clause conditions first.

Conclusion

The issue of SQL Server not updating records with nested case statements often comes down to improper null checking. By correcting your syntax to use IS NULL, you can ensure your queries execute as intended, updating records in your database successfully.

By following these best practices, you'll be better equipped to write effective SQL statements and avoid common pitfalls. Happy querying!