Second Normal Form (2NF)
Definition - What does Second Normal Form (2NF) mean?
Normalization is the process of organizing data in a database so that it meets two basic requirements:
- There is no redundancy of data (all data is stored in only one place).
- Data dependencies are logical (all related data items are stored together).
Techopedia explains Second Normal Form (2NF)
- Split up all data resulting in many-to-many relationships and store the data as separate tables. For example, in a database used by a school’s application, two of the tables are STUDENT and SUBJECT. In real life, a student takes several subjects simultaneously while a subject is studied by several students. These are many-to-many relationships. 2NF states that this relationship must be split into more than the two tables above (STUDENT and SUBJECT). One way of splitting them is by introducing a third table, which contains the columns Student_ID, Subject_ID, Semester and Year. In this way, there is no direct relationship between STUDENT and SUBJECT because all relationships are created indirectly through the third table.
- Create relationships between tables by use of foreign keys. For example, a bank’s database contains two tables: CUSTOMER_MASTER (for storing customer details) and ACCOUNT_MASTER (for storing details about bank accounts, including which customer holds which account). There must be a way to link the two tables to know who the customer is for each account. The way to do this is via a foreign key, which is a column in the ACCOUNT_MASTER table pointing to a corresponding column in the CUSTOMER_MASTER table.
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