SQL allows a foreign-key dependency to refer to the same relation, as in thefollowing example:create table manager(employee ID char(20),manager ID char(20),primary key employee ID,foreign key (manager ID) references manager(employee ID)on delete cascade )Here, employee_ID is a key to the table manager, meaning that each employeehas at most one manager. The foreign-key clause requires that every manageralso be an employee. Explain exactly what happens when a tuple in the relationmanager is deleted.
SQL allows a foreign-key dependency to refer to the same relation, as in thefollowing example:create table manager(employee ID char(20),manager ID char(20),primary key employee ID,foreign key (manager ID) references manager(employee ID)on delete cascade )Here, employee_ID is a key to the table manager, meaning that each employeehas at most one manager. The foreign-key clause requires that every manageralso be an employee. Explain exactly what happens when a tuple in the relationmanager is deleted.
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
Problem 1PE
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SQL allows a foreign-key dependency to refer to the same relation, as in the
following example:
create table manager
(employee ID char(20),
manager ID char(20),
primary key employee ID,
foreign key (manager ID) references manager(employee ID)
on delete cascade )
Here, employee_ID is a key to the table manager, meaning that each employee
has at most one manager. The foreign-key clause requires that every manager
also be an employee. Explain exactly what happens when a tuple in the relation
manager is deleted.
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