Sql server ___________session3-normailzation
Download as PPTX, PDF0 likes332 views
Normalization is the process of organizing data in a database to minimize redundancy and dependency. It involves breaking tables into smaller tables and linking them through relationships. The goals are to eliminate storing duplicate data, ensure related data is stored together, and reduce data anomalies. Normalization is achieved through three normal forms - 1NF, 2NF, and 3NF - which introduce rules to simplify attributes, eliminate partial dependencies, and remove transitive dependencies.
Sql server ___________session3-normailzation
- 2. Normalization Normalization is the process of efficiently organizing data in a database. Normalization is the process of applying a series of rules to ensure that your database achieves optimal structure.
- 3. Why we do Normalization? There are two goals of the normalization process: 1- eliminating redundant data For example: storing the same data in more than one table 2- ensuring data dependencies make sense. For example: only storing related data in a table. Both of these are worthy goals as they reduce the amount of space a database consumes and ensure that data is logically stored.
- 4. Database Anomalies: Repetition Anomaly Insertion Anomaly Deletion Anomaly Updating Anomaly
- 5. First Normal Form (1NF) Each attribute must be atomic • No repeating columns within a row. • No multi-valued columns. 1NF simplifies attributes • Queries become easier.
- 6. 1NF Employee (unnormalized) emp_no emp_name project_id project_name grade salary 142 John 113, 124 blue star, magnum A 20,000 168 James 113 blue star B 15,000 263 Andrew 113 blue star C 10,000 Employee (1NF) emp_no emp_name project_id project_name grade salary 142 John 113 blue star A 20,000 142 John 124 magnum A 20,000 168 James 113 blue star B 15,000 263 Andrew 113 blue star C 10,000
- 7. Second Normal Form (2NF) Each attribute must be functionally dependent on the primary key. • Partial Functional dependency – a non-key attribute should not be partially(functionally) dependent on more than one key attribute. • Any non-dependent attributes are moved into a smaller (subset) table. 2NF improves data integrity. • Prevents update, insert, and delete anomalies.
- 8. Functional Dependency Emp_name, grade and salary are functionally dependent only on emp_no. (emp_no -> emp_name, grade, salary) Project_name is dependent only on project_id. But these table should be related through foreign keys. emp_no emp_name grade salary 142 John A 20,000 168 James B 15,000 263 Andrew C 10,000 109 Bob C 10,000 Employee (1NF) Project (1NF) project_id project_name 113 blue star 124 magnum
- 9. 2NF emp_no emp_name grade salary 142 John A 20,000 168 James B 15,000 263 Andrew C 10,000 109 Bob C 10,000 Employee (2NF) Project (2NF) project_id project_name 113 blue star 124 magnum
- 10. Data Integrity • Insert Anomaly - adding null values. eg, inserting a new project does not require the primary key of emp_no to be added. • Update Anomaly - multiple updates for a single name change, causes performance degradation. eg, changing magnum project_name to meganum. • Delete Anomaly - deleting wanted information. eg, deleting the magnum project removes employee John personal info from the database.
- 11. Third Normal Form (3NF) Remove transitive dependencies. •Transitive dependency – if an attribute can be determined by another non-key attribute. • Any transitive dependencies are moved into a smaller (subset) table. 3NF further improves data integrity. • Prevents update, insert, and delete anomalies.
- 12. Transitive Dependency salary is determined by grade and not the key attribute emp_no. Thus this transitive dependency needs to be removed, and grade and salary are moved to another table. emp_no emp_name grade salary 142 John A 20,000 168 James B 15,000 263 Andrew C 10,000 109 Bob C 10,000 Employee (3NF)
- 13. 3NF emp_no emp_name grade 142 John A 168 James B 263 Andrew C 109 Bob C Employee (3NF) Project (3NF) project_id project_name 113 blue star 124 magnum Employee Project(3NF) emp_no project_name 142 113 142 124 168 113 263 113 109 124 Grade Salary(3NF) grade salary A 20,000 B 15,000 C 10,000
- 14. Denormalization Denormalization is a technique to move from higher to lower normal forms of database modeling in order to speed up database access.
Editor's Notes
- #13: Note, dept_name is functionally dependent on dept_no. Dept_no is functionally dependent on emp_no, so via the middle step of dept_no, dept_name is functionally dependent on emp_no. (emp_no -> dept_no , dept_no -> dept_name, thus emp_no -> dept_name)