Скачать или смотреть Tansy SQL Course | NUll vs NOT NULL | Chapter 5 | Lesson 6

In SQL, `NULL` represents the absence of a value or an unknown value in a column, whereas `NOT NULL` is a constraint that ensures a column cannot contain `NULL` values. When a column is defined with `NULL`, it can store missing or undefined values, but when defined as `NOT NULL`, every row must contain a valid value in that column. The `NOT NULL` constraint is commonly used for columns that must always have data, such as primary keys or essential attributes.

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