Defining a Null Value
A null value is undefined , unavailable, unassigned, unknown. It is not equal to zero or blank space . It is simply nothing.
In SQL statement if any row doesn't have data, then it is said to be null.
Any arithmetic expression using NULL values results into NULL.
Any column can have null data, but the constraints NOT NULL and Primary key does't allow null values in its columns.
Queries using nulls:
Any arithmetic operation with null results in null
NULL comparison with NULL yields null
Below query gives the employee's whose commission is null
Queries using nulls:
Any arithmetic operation with null results in null
NULL comparison with NULL yields null
Below query gives the employee's whose commission is null
