Difference between Primary Key and Foreign Key
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Duplication Tuples can have a duplicate value for a foreign key attribute. The primary key constraint can be defined on a temporary table. Makes sense, but wait!
The value of the primary key attribute should never or rarely changed. What is the point of having a foreign key? And how does SAP ERP software...
Difference between Primary Key and Foreign Key - BusinessEntityID, in the other table. Do you want your primary key to rely on government data?
By the way, what is a foreign key in a table and difference between Primary and Foreign key are some of the popular SQL interview questions, much like or? We have been learning key SQL concepts along with these frequently asked SQL questions and in this SQL tutorial, we will discuss what is a foreign key in SQL and purpose of the foreign key in any table. By the way, this is the third article related to a primary key in SQL, other being and. If you are preparing for any technical job interview where you expect some SQL questions, check out these questions, they are worth preparing. A Foreign key is a column in one table which is the primary key on another table. Foreign key and a Primary key is used to define relationship between two tables in relational database. Foreign key in a table enforce , which can be used to implement business rules e. This kind of check maintains integrity of data in a relationship. As discussed in our post , we have seen that it's implemented as foreign key constraint and can allow CASCADE UPDATE and DELETE. These referential action delete or update matching column in child table foreign key table when corresponding row from parent table primary key table is deleted or updated to maintain integrity of data. It could have been different e. This is one of the benefit of using Referential Integrity. It also allow to CASCADE UPDATE and DELETE operation which first delete or update a row in parent table e. Customer and then delete or update all matching rows in child table e. That's all on what is foreign key in a table and difference between primary and foreign key in SQL. I suggest to create some table by yourself and try to test foreign key constraint by violating it and see how database e. Oracle, MySQL or SQL Server behaves. To understand more try ON DELETE CASCADE and ON DELETE UPDATE to see how database maintains foreign key constraint. You can also see my post on Further Learning.
In order to be a primary key, several conditions must hold true. Change in any attribute value of primary key would create confusion. A primary key is a table column that can be used to uniquely identify every row of the table. It refers to a column or a group of columns that uniquely identifies a row of another table or same table. Foreign keys and referential integrity Foreign keys have a lot to do with the concept of referential integrity. It seems like two different ways of doing the same thing, even though one uses a composite primary key and the other uses a foreign key. A Foreign key is a column in one table which is the primary key on another table. Can a foreign key contain null values?.
