What is the expression of null value in sql?

Null values ​​in SQL are represented as NULL, which means that the value does not exist or is unknown. It is different from 0 or an empty string. NULL can be compared with any data type, but behaves as false in logical operations. Ignored in some aggregate functions, such as SUM() and COUNT(). It should be noted that NULL cannot be equal to other values, cannot be used in mathematical operations, and may lead to inaccurate results in some cases.

Representation of null value in SQL

NULL is used in SQL to represent null value.

Meaning

NULLIndicates that a value does not exist or is unknown. It is different from the value 0 or the empty string because 0 is a valid value and the empty string is a non-null value.

Compare using

• : NULL can be compared with any data type, and the result is always NULL.
• Logical operations: NULL behaves as a false value in logical operations.
• Aggregation functions: NULL is ignored in some aggregate functions, such as SUM() and COUNT().

Note

• NULL cannot be equal to other values ​​(even NULL).
• NULL cannot be used in mathematical operations as this will return NULL.
• In some cases, NULL may lead to inaccurate query results, so care should be taken when using it.

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