Null vs. Empty — What's the Difference?

Null is a term frequently used in programming to indicate the absence of a value or the absence of a reference. It represents an undefined state or an uninitialized variable. In databases, a null value indicates that a particular field has no value or is undefined. Empty, conversely, is used to denote that a given object, string, or data structure has been initialized but contains no elements or meaningful data. In databases, an empty field would be one that has been initialized but contains no information.

When you encounter the term "null," it usually means that the variable or object in question has not been assigned any value or object. It's a placeholder for "nothing" or "unknown." Empty, however, means that the variable or object has been assigned a value, but that value has no length or elements. For instance, an empty array has been initialized but has zero elements.

Null and empty serve different purposes and are often not interchangeable. For example, in programming languages like JavaScript, a variable can be null, but it cannot be null and empty at the same time. Checking for null and empty conditions often requires separate conditional statements. In SQL databases, a null value in a field means the absence of data, while an empty string might be used to indicate that the data is known to be blank.

In practical use, null is often used for object references or pointers that should not point to any location in memory. It's like saying, "This pointer points to nowhere." On the other hand, empty is like saying, "This container exists, but it's currently holding nothing." While both concepts are related to the absence of data, null usually indicates a more fundamental lack of definition than empty.