| The NULL value |
|
|
|
|
|
|
|
|
|
|
| • | NULL
marks an attribute undefined |
||||||||
| • | NULL
is a valid value of ANY data type |
||||||||
| • | Unspecified
attributes get the NULL value |
||||||||
| • | NULL
is not equal to any value |
||||||||
| but |
|||||||||
| NULL
is equivalent to NULL |
|||||||||
| • | The
function NVL(x,y) returns y if x |
||||||||
| equivalent
NULL, else it returns x |
|||||||||