Difference between Primary Key and Foreign Key
Primary Key:
A primary key is used to ensure data in the specific column is unique. It is a column cannot have NULL values. It is either an existing table column or a column that is specifically generated by the database according to a defined sequence.
Example: Refer the figure –
STUD_NO, as well as STUD_PHONE both, are candidate keys for relation STUDENT but STUD_NO can be chosen as the primary key (only one out of many candidate keys).
Foreign Key:
A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables. It is a column (or columns) that references a column (most often the primary key) of another table.
Example: Refer the figure –
STUD_NO in STUDENT_COURSE is a foreign key to STUD_NO in STUDENT relation.
Figure:
Let’s see the difference between Primary Key and Foreign Key:
| S.NO. | PRIMARY KEY | FOREIGN KEY |
|---|---|---|
| 1 | A primary key is used to ensure data in the specific column is unique. | A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables. |
| 2 | It uniquely identifies a record in the relational database table. | It refers to the field in a table which is the primary key of another table. |
| 3 | Only one primary key is allowed in a table. | Whereas more than one foreign key are allowed in a table. |
| 4 | It is a combination of UNIQUE and Not Null constraints. | It can contain duplicate values and a table in a relational database. |
| 5 | It does not allow NULL values. | It can also contain NULL values. |
| 6 | Its value cannot be deleted from the parent table. | Its value can be deleted from the child table. |
| 7 | It constraint can be implicitly defined on the temporary tables. | It constraint cannot be defined on the local or global temporary tables. |
GeeksforGeeks has prepared a complete interview preparation course with premium videos, theory, practice problems, TA support and many more features. Please refer Placement 100 for details
Recommended Posts:
- Types of Keys in Relational Model (Candidate, Super, Primary, Alternate and Foreign)
- Difference between Primary key and Super key
- Difference between Primary and Candidate Key
- Difference between Primary key and Unique key
- Difference between Primary and Secondary Memory
- Difference between JSP and ASP
- Difference between RAM and ROM
- Difference between T-SQL and PL-SQL
- Difference between LED and LCD
- Difference between C and C#
- What is the difference between GUI and CUI?
- Difference between CD-R and CD-RW
- Difference Between Gi-Fi and Li-Fi
- Difference between Tor and VPN
- Difference between USB 2.0 and USB 3.0
If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.
