Can you explain the meaning of null in the context of databases?

In the context of databases, a null value indicates the absence of data or an unknown value in a specific field. It is not the same as zero or an empty string — null indicates that the value is simply not set.

For example, if a user does not have a specified phone number, the "phone" field will be null. This is important to consider when querying and processing data, as operations with null can behave differently (for example, comparing with null returns unknown).

In SQL, to check for null, the constructs IS NULL or IS NOT NULL are used:

SELECT * FROM users WHERE phone IS NULL;

Thus, null helps accurately reflect the absence of information in the database.