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Can Super key be null?
why there is no answer yet
Have foreign keys null values?
Yes Foreign key can have null value.
Can a primary key have a blank or null value entered into its cell?
No. A Primary Key is the Unique identifier and cannot be null and cannot be duplicate.
Can you use more than one null value for unique key?
No.
Does primary key allows null value?
No. A primary key requires a value because it is the field that all other values in the row depend on.
What rule states that either each foreign key value must match a primary key value in another relation or the foreign key value must be null?
referential integrity constraint
Entity integrity constraint?
The entity integrity constraint states that no primary key value can be null. This is because the primary key value is used to identify individual tuples in a relation. Having null value for the primary key implies that we cannot identify some tuples. This also specifies that there may not be any duplicate entries in primary key column key row.
Explain two rules in relational model of database systems?
1) Entity Integrity: In a base relation, no attribute of a primary key can be null. 2) Referential Integrity: If foreign key exists in a relation, either foreign key value must match a candidate key value of some tuple in its home relation or foreign key value must be wholly null
Can a foreign key be null?
yes .a foreign key can have null values
What is the difference between an array shift and unsetting a variable in PHP?
By shifting the values in an array, you are moving a key's value to the previous key. The very first key's value is obliterated. By shifting all values in the array, all keys will have a value of NULL. Unsetting a variable is entirely different -- performing a variable unsetting causes the variable to have a value of NULL, as if it was never set.
Can unique key be null?
No unique can not be nulll....unique must have any unique value for unique identification.,...
What is difference between null value and not null value?
In databases: Null Value: Represents the absence of a value or an unknown value. It indicates that the data is missing or not applicable. Not Null Value: Indicates that a field contains a valid, defined value. It means the data is present and has been explicitly set.
