A foreign key is a column or can also be a combination of multiple columns in a relational database that has links to data in two tables.
Post 1
A foreign key is a column or can also be a combination of multiple columns in a relational database that has links to data in two tables. A foreign key is a cross-reference between two tables that references the primary key of another table. When there is a foreign key relationship with the primary key then the primary key is considered as a parent and the foreign key is considered as a child, in this case, the parent which is the primary key cant be missing if there exists a foreign key. Also foreign key column cant be a computed column (Elmasri & Navathe, 2016).
The primary key can be easily enforced in DBMS on the primary table by setting the primary key constraint. In the same manner, a foreign key can be enforced on the table by referencing the primary key. eg. When there is an Employee table then Employee_ID can be made a primary key and in the other table Department, we can create Employee_ID in that which will act as a foreign key. So in this case every department entered if there exists a foreign key value then the primary key value will always exist. It\\\’s always good to avoid null values in the foreign keys (Elmasri & Navathe, 2016). To enforce the integrity foreign key should be enforced with no null values if there is a null value in the foreign key then it won\\\’t be checked with the primary table and it\\\’s not difficult to implement this.
Constraints can be executed in an efficient manner when data updates are happening, but we need to follow the definition of the constraints when designing the database. Constraints, if designed properly, will add great integrity to the database and if not designed and implemented in the correct way can degrade the performance of the database.
Post 2
A foreign key is a column or can also be a combination of multiple columns in a relational database that has links to data in two tables. A foreign key is a cross-reference between two tables that references the primary key of another table. When there is a foreign key relationship with the primary key then the primary key is considered as a parent and the foreign key is considered as a child, in this case, the parent which is the primary key cant be missing if there exists a foreign key. Also foreign key column cant be a computed column (Elmasri & Navathe, 2016).
The primary key can be easily enforced in DBMS on the primary table by setting the primary key constraint. In the same manner, a foreign key can be enforced on the table by referencing the primary key. eg. When there is an Employee table then Employee_ID can be made a primary key and in the other table Department, we can create Employee_ID in that which will act as a foreign key. So in this case every department entered if there exists a foreign key value then the primary key value will always exist. It\\\’s always good to avoid null values in the foreign keys (Elmasri & Navathe, 2016). To enforce the integrity foreign key should be enforced with no null values if there is a null value in the foreign key then it won\\\’t be checked with the primary table and it\\\’s not difficult to implement this.
Constraints can be executed in an efficient manner when data updates are happening, but we need to follow the definition of the constraints when designing the database. Constraints, if designed properly, will add great integrity to the database and if not designed and implemented in the correct way can degrade the performance of the database.
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