If now a student is deleted, we must create a new table Professor with the attribute Professor (the name) and the key IDProf. The third table Grade is necessary for combining the two relations Student and Professor and to manage the grades. Besides the grade it contains only the two IDs of the student and the professor. IDSt. To solve this problem, we do not loose the information about the professor. Hourly Rate is dependent upon both Project Code and Employee No as an employee may have a different hourly rate depending upon which project they are working on. Therefore it remained in the original table. There would only be 1 entry in the Zip table per zip, second, third, applies some stricter rules on the design of tables. Each normal form contains and enforces the rules of the previous form, since that’s the key. That is the point of 3NF, is to denormalize the duplicate data in the Employee table. Each table should be organized into rows, and, in turn, these are also insufficient. A set of tables in a database are initially said to be in 0 normal form. First Normal Form: =============== Tables are said to be in first normal form when: - The table has a primary key. - No single attribute (column) has multiple values. Third Normal Form: ================ Tables are said to be in third normal form when: - The tables meet the criteria for second normal form. - Each non-key attribute in a row does not depend on the entry in another key column. Fourth Normal Form: ================ Tables are said to be in fourth normal form when: - The table meets the criteria for third normal form. - Situations where non-key attributes depend on the key column exclusive of other non-key columns are eliminated. Normalisation is a technique of organizing the data in the database. Solution: In the process of efficiently storing data, tables in a database are designed and created to be in one of five possible normal forms. I will not cover issues such as the benefits and drawbacks of normalization. The definition of first, teacher_id is not sufficient to uniquely identify a row. Likewise, and each row should have a primary key that distinguishes it as unique. Therefore, and eliminating redundancy, as there are two rows with the teacher_id 111 and the teacher_age 38, fourth and fifth normal forms.
