Concept explainers
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.
One-to-Many Relationship:
When one record in a database table is associated with more than one record in another table, the relationship between the two tables is referred as one-to-many relationship. It is also represented as1: M relationship. This is the opposite of many to one relationship.
One-to-One relationship:
When one record in a database table is associated with one and only one record in another table, the relationship between the two tables is referred as one-to-one relationship. It is also represented as1: 1 relationship.
ENTITY- RELATIONSHIP DIAGRAM (ERD):
Entity- Relationship Diagram is also known as ER 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.
CROW FOOT ERD:
The Crow Foot ERD is an Entity Relationship Diagram which is used to represent the cardinalities present in the basic ER diagram. It is used to represent the relationships present between two tuples or tables present in the database.
Given database tables:
Table Name: EMPLOYEE
| EMP_CODE | EMP_TITLE | EMP_LNAME | EMP_FNAME | EMP_INITIAL | EMP_DOB | STORE_CODE |
| 1 | Mr. | Williamson | John | W | 21-May-84 | 3 |
| 2 | Ms. | Ratula | Nancy | 09-Feb-89 | 2 | |
| 3 | Ms. | Greenboro | Lottie | R | 02-Oct-81 | 4 |
| 4 | Mrs. | Rumpersfro | Jennie | S | 01-Jun-71 | 5 |
| 5 | Mr. | Smith | Robert | L | 23-Nov-59 | 3 |
| 6 | Mr. | Renselear | Cary | A | 25-Dec-85 | 1 |
| 7 | Mr. | Ogallo | Roberto | S | 31-Jul-82 | 3 |
| 8 | Ms. | Johnson | Elizabeth | I | 10-Sep-88 | 1 |
| 9 | Mr. | Eindsmar | Jack | W | 19-Apr-55 | 2 |
| 10 | Mrs. | Jones | Rose | R | 06-Mar-66 | 4 |
| 11 | Mr. | Broderick | Tom | 21-Oct-72 | 3 | |
| 12 | Mr. | Washington | Alan | Y | 08-Sept-74 | 2 |
| 13 | Mr. | Smith | Peter | N | 25-Aug-64 | 3 |
| 14 | Ms. | Smith | Sherry | H | 25-May-66 | 4 |
| 15 | Mr. | Olenko | Howard | U | 24-May-64 | 5 |
| 16 | Mr. | Archialo | Barry | V | 03-Sep-60 | 5 |
| 17 | Ms. | Grimaldo | Jeanine | K | 12-Nov-70 | 4 |
| 18 | Mr. | Rosenburg | Andrew | D | 24-Jan-71 | 4 |
| 19 | Mr. | Rosten | Peter | F | 03-Oct-68 | 4 |
| 20 | Mr. | Mckee | Robert | S | 06-Mar-70 | 1 |
| 21 | Ms. | Baumann | Jennifer | A | 11-Dec-74 | 3 |
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 |
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Chapter 3 Solutions
Database Systems: Design, Implementation, & Management
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