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RDBMS terminologies
RDMS Terminologies include Database, Table, Columns, etc. Let us see them one by one −
Database
Database is a collection of tables like <Student>, <Professors>, etc.
Table
A table is a collection of rows and columns , for example,
|
StudentId |
StudentName |
StudentRank |
| 052 |
Tom |
1 |
| 035 |
David |
2 |
| 077 |
John |
3 |
Column
Column is in a table −
Row
Row is also called a tuple in RDBMS.
A relation in a database has rows and columns.
Primary Key
Every table has one Primary key and cannot have null values.
For example, ProjectID is a primary key in Project Table, since it uniquely identifies the project:
|
ProjectID |
ProjectName |
| P01 |
Cluster Grouping System |
| P02 |
Hospital Management System |
Foreign Key
If you want to link two tables, use Foreign Key.
For example, Employee table has DEPT_ID that is a foreign key, which is linked to Department table.
The Department table has primary key DEPT_ID.
Super Key
Super Key is an attribute (or a set of attributes) that uniquely identify a tuple i.e. an entity in entity set. It is a superset of Candidate Key, since Candidate Keys are selected from super key.
Composite Key
A primary key having two or more attributes is called composite key. It is a combination of two or more columns.
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