The Concept of Null: Why It's Not Equal to Anything, Even Itself скачать в хорошем качестве

The Concept of Null: Why It's Not Equal to Anything, Even Itself

Explore the concept of `Null` in programming languages, understand its meaning as an unknown value, and discover its implications in SQL and beyond. --- This video is based on the question https://stackoverflow.com/q/75267/ asked by the user 'cazlab' ( https://stackoverflow.com/u/6178/ ) and on the answer https://stackoverflow.com/a/75314/ provided by the user 'Jonathan Rupp' ( https://stackoverflow.com/u/12502/ ) 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, comments, revision history etc. For example, the original title of the Question was: In how many languages is Null not equal to anything not even Null? 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 2.5' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 2.5' ( https://creativecommons.org/licenses/... ) license. If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com. --- Understanding Null: An Intriguing Quirk in Programming Languages When venturing into the world of programming and databases, one frequently encounters the concept of null. However, a perplexing question arises: In how many languages is Null not equal to anything, not even Null itself? This question goes beyond a simple puzzle; it touches on the fundamental differences in how languages treat null and its implications for developers. What Does Null Mean? In the realm of programming, null can represent a couple of different concepts, depending on the context and the programming language being used. Here’s a brief overview: In SQL (Structured Query Language): null represents an unknown or undefined value. When you encounter null in SQL, it signifies that the information is missing. Therefore, any operations involving null will also yield null. This leads us to our main point: null in SQL is not equal to null. In many programming languages (like C++ or C): null signifies the absence of a value, specifically a pointer or reference that doesn't point to any object. In these cases, two null pointers are equivalent—both denote nothing. This fundamental difference between null as an unknown versus null as the absence of value is crucial to understanding how different languages handle comparisons involving null. Why the Confusion? The confusion arises from the use of the same term: null. Different languages—and even different contexts within those languages—assign varying meanings and implications to null. Here’s a breakdown of these points: Unknown vs. Nothing: In SQL, null stands for an unknown, so the logic dictates that any operation involving null yields an "unknown" result. Therefore, even comparing null to itself leads to an unknown outcome. In contrast, in languages like C++ or C, null is a defined value that denotes "nothing." Thus, when two null values are compared, they are considered equivalent. Language Specificity: Understanding how null is treated in a specific programming language is crucial. Certain languages have built-in functionality to handle null, while others may require additional logic to prevent issues stemming from null comparisons. Practical Implications of Null Understanding how to work with null can significantly affect your programming practices and database interactions. SQL: Always remember that in SQL, you cannot rely on null being equal to anything. Using functions like IS NULL or employing the COALESCE function can allow you to manage null values more effectively. Programming Languages: Whether you're working with pointers in C++ or references in C, it's important to check for null before performing operations to avoid unexpected behaviors or errors. Conclusion The concept of null, while seemingly simple, holds layers of complexity that varies between SQL and programming languages. Recognizing these differences not only helps alleviate confusion but also empowers developers to make informed choices when working with data and code. By understanding why null is not equal to anything—not even null itself—you’re better equipped to handle the quirks of programming and database design. Remember, next time you encounter null, take a moment to reflect on its meaning in your context—whether it’s an unknown or a nothing. Embrace the intricacies of programming, and your code will benefit from that understanding.