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.
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.
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.
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Chapter 3 Solutions
EBK DATABASE SYSTEMS: DESIGN, IMPLEMENT
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- Count the number of different professors names.arrow_forwardQ1: Show all the information from the employee table. SELECT * FROM emp; Q2: Show the employees names and numbers from employee table. SELECT empname, Empno FROM emp; Q3: Show the employees names, salaries and their annual salaries from the employee table, name the last field by annual salary. SELECT empname, sal, sal*12 FROM emp; Or we can change the attribute name using as SELECT empname, sal, sal*12 as "Annual Salary" FROM emp; Q4: Show the employees names, salaries, salaries plus commotion for each employees from employee table. SELECT empname, sal, sal+tcommotion FROM emp; Q5: Show the employees names, salaries, annual salaries plus 100$ for each employees from employee table. SELECT empname, sal, (sal*12)+100 FROM emp; Q6: Retrieve the hire date and department number of the employee(s) whose name is “John" WHERE SELECT hiredate, deptno FROM John'; %3D emp empname Q7. Retrieve the name and job title of all employees who work for the department number 10. SELECT empname, job FROM…arrow_forwardWEEK 9 ASSIGNMENT#3 Part I: Complete the following exercise: Create the following table with the correct columns. Call your new table: student_course (see below). Populate this table with four rows. Make sure the student id column contains values that are also in the student id column of your student table. student id course id semester year Join the student and student_course table where the student id values are the same. Join the student and student_course table where the student id values are the same and year is equal to 2020. Create a select statement that will return the length of the last name column by joining the student and student_course table where the student id values are the same and enroll month is June. Once you have completed your assignment, copy and paste the script into a Word document. Part II: Complete the following exercise: Using a subquery, select student first name where the student is in the student course table. Using a subquery, select the…arrow_forward
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