Primary Key:
A Primary Key in a
Example:
Students in Universities are assigned a unique registration number.
Therefore, in a STUDENT database table, the attribute “reg_no” acts as primary key.
Foreign Key:
Foreign Key is a column in a relational database table which provides a relation between two tables. It provides a cross reference between tables by pointing to primary key of another table.
Example:
In STUDENT database table, the attribute “reg_no” acts as primary key and in COURSE database table in which the student selects his or her course, the same “reg_no” acts as foreign key for the STUDENT table.
Many to one relationship:
When one record in a database table is associated with one or more records in another table, the relationship between the two tables is referred as many to one relationship. It is also represented as M:1 relationship.
RELATIONAL DIAGRAM:
Relational Diagram is also known as Entity Relational Diagram. It is used to define the conceptual view of the database as viewed by the end user. It is used to depict the database’s main components: entities, relationships and attributes. It describes how data is related to each other.
Given database tables:
Table Name: STORE
STORE_CODE | STORE_NAME | STORE_YTD_SALES | REGION_CODE | EMP_CODE |
1 | Access Junction | 1003455.76 | 2 | 8 |
2 | Database Corner | 1421987.39 | 2 | 12 |
3 | Tuple Charge | 986783.22 | 1 | 7 |
4 | Attribute Alley | 944568.56 | 2 | 3 |
5 | Primary Key Point | 2930098.45 | 1 | 15 |
Table Name: REGION
REGION_CODE | REGION_DESCRIPT |
1 | EAST |
2 | WEST |
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Database Systems: Design, Implementation, & Management
- Database Systems: Design, Implementation, & Manag...Computer ScienceISBN:9781305627482Author:Carlos Coronel, Steven MorrisPublisher:Cengage LearningDatabase Systems: Design, Implementation, & Manag...Computer ScienceISBN:9781285196145Author:Steven, Steven Morris, Carlos Coronel, Carlos, Coronel, Carlos; Morris, Carlos Coronel and Steven Morris, Carlos Coronel; Steven Morris, Steven Morris; Carlos CoronelPublisher:Cengage Learning