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
- :
NULLcan be compared with any data type, and the result is alwaysNULL. - Logical operations:
NULLbehaves as a false value in logical operations. - Aggregation functions:
NULLis ignored in some aggregate functions, such asSUM()andCOUNT().
Note
-
NULLcannot be equal to other values (evenNULL). -
NULLcannot be used in mathematical operations as this will returnNULL. - In some cases,
NULLmay lead to inaccurate query results, so care should be taken when using it.
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