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 more than one record in a database table is associated with only one record 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.
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.
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Chapter 3 Solutions
Database Systems: Design, Implementation, & Management
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- An EMPLOYEES table was added to the JustLee Books database to track employee information. Display a list of each employee’s name, job title, and manager’s name. Use column aliases to clearly identify employee and manager name values. Include all employees in the list and sort by manager name.arrow_forwardWrite the SQL code to create the table structures for the entities shown in Figure P7.65. The structures should contain the attributes specified in the ERD. Use data types that are appropriate for the data that will need to be stored in each attribute. Enforce primary key and foreign key constraints as indicated by the ERD.arrow_forward
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