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In databases:
Null Value: Represents the absence of a value or an unknown value. It indicates that the data is missing or not applicable.
Not Null Value: Indicates that a field contains a valid, defined value. It means the data is present and has been explicitly set.
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LaoNull value: In database terminology, a null value indicates that the field or column does not have a value. It may indicate either the data are missing, or that it is unknown. A column that can be null contains that column holding a value of null in any particular column. Null does not equal zero or an empty string.
NOT NULL value: This specifies that some field or column in the database must contain some value. It enforces an obligation such that the data in the said field cannot be blank or null. A column that has been defined as "not null" must at all times contain a valid value, and it cannot remain blank.
In brief, the null is no data or unknown data values. On the other hand, not null indicates that a field should not be empty but rather must contain some valid value.
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Difference between void pointer and null pointer?
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What is the difference between call by value and call by name in programming languages?
In call by value, the value of the argument is passed to the function, while in call by name, the expression for the argument is passed and evaluated each time it is used in the function.
