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Yes Foreign key can have null value.
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∙ 15y ago
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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.
Can a foreign key be null?
yes .a foreign key can have null values
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.
What are the various reasons that lead to the occurrence of NULL values in relations?
A given field in a database table might be for a values that, in certain case, no such values exist or can be determined. For example, in an employee database, a field might be a foreign key to that employee's direct manager. However, in the case of the CEO, there is no such person. In that case, the field would be set to Null.
When was Foreign Keys created?
Foreign Keys was created in 1985.
What is contraints?
Constraint, in Project Management terms, means a factor that affects when an activity can be scheduled. ------------------------------------------------------------------------------------------ It can be some kind of a limitation or restriction. webmaster at service.ztronics.com ------------------------------------------------------------------------------------------ Since this question has been categorised in Database Design, I will assume you mean what is a a constraint within a database... You can have primary key, foreign key, alternate key and domain (aka check) constraints. Domain contraints apply to a single field in a single row - e.g. whether or not nulls are allowed, or an enumerated list of allowed values. Primary keys and alternate keys ensure that a for the column(s) in the key each row in the table has a unique value (or set of values if the key is composite). Foreign keys ensure that if one table references another, that the reference exists in the parent table. This is normally linked to the primary key e.g. this example (Oracle syntax) demonstrates these create table employee ( employee_id number not null, first_name varchar2(100) not null, middle_names varchar2(100) null, last_name varchar2(100) not null, sex char(1), ni_number varchar2(10) not null, CONSTRAINT pk_employee PRIMARY KEY (employee_id), CONSTRAINT ak_national_insurance UNIQUE (ni_number), CONSTRAINT cc_sex CHECK sex in ('M', 'F') ); create table emp_salary_hist ( employee_id number not nul,l pay_review date not null, pay_grade number not null, salary number not null, CONSTRAINT pk_emp_sal_hist PRIMARY KEY (employee_id, pay_review), CONSTRAINT fk_employee FOREIGN KEY (employee_id) REFERENCES employee(employee_id) );
Did Group functions include nulls in calculations?
no null values will not be included explanation when oracle parse the query the null values will be omitted for some reason if you want to consider null values you have to use some oracle functions like nvl or nvl2
Can the foreign key accept null?
yes
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.
What are the three interpretations for null values?
In a database it can be 'not known' or 'not applicable'.
Is the critical region the values of the test statistics for which the null hypothesis will reject?
The null hypothesis will not reject - it is a hypothesis and is not capable of rejecting anything. The critical region consists of the values of the test statistic where YOU will reject the null hypothesis in favour of the expressed alternative hypothesis.
What is the difference between LinkedList and Hashtable?
A linked list is made up of a sequence of connected (linked) nodes. A hashtable is usually backed by an array, and is an association of keys and values. When an object is added to the array it becomes a value; the object is hashed to get a key (an index into the array).
