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Can a foreign key be null?
yes .a foreign key can have null values
Have foreign keys null values?
Yes Foreign key can have null value.
Does foreign key alllows null values and duplicate values?
A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.
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
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
Difference between foreign key and composite key?
primary key: primary creates a clustered index on the column and it doesn't allow null values. unique key: unique key creates non clustered index by default.it allows "one null value". foreign key: A foreign key (FK) is a column or combination of columns used to establish and enforce a link between the data in two tables. Fore More information, you can visit this website:http://www.iyogibusiness.com
What the differences between primary key and foreign key?
A primary key is a unique identifier for a record in a table and ensures each record is uniquely identified. A foreign key establishes a relationship between two tables by referencing the primary key in another table. It enforces referential integrity by ensuring that the values in the foreign key column correspond to values in the primary key column of another table.
How do you apply a foreign key in a database?
The foreign key is a reference to a key (identifier) of a row in another or even the same table. When the foreign key is not null, it implies that there's an entry in the referenced table with that identifier. The syntax depends on wich database are you using, check the page in the related links below.
When you accept the Null Hypothesis you are certain that the Null Hypothesis is correct?
No, you are never certain.
What is a primary key that is null?
Unique key
What is the difference between primary key and secondary key?
There is two difference between them. 1. The not null constraint is by default added to primary key, it means, primary key attribute cannot accept null values, whereas, the attribute declared as unique can accept null values. It is the major difference between the two. 2. Secondly, we can have only one primary key in a relation, whereas, multiple attributes can be declared unique at the same time.
What not a likely primary key?
A field that is not unique and null can not be used as a primary key. Praimary key must satisfy the conditions of not null and unique.
