david2999999 / SQL

SQL (pronounced "ess-que-el") stands for Structured Query Language. SQL is used to communicate with a database. According to ANSI (American National Standards Institute), it is the standard language for relational database management systems. SQL statements are used to perform tasks such as update data on a database, or retrieve data from a database. Some common relational database management systems that use SQL are: Oracle, Sybase, Microsoft SQL Server, Access, Ingres, etc.

First Normal Form (1NF)

• It should only have single(atomic) valued attributes/columns.
• Values stored in a column should be of the same domain
• All the columns in a table should have unique names.
• And the order in which data is stored, does not matter.

Second Normal Form (2NF)

• For a table to be in the Second Normal form, it should be in the First Normal form and it should not have Partial Dependency.
• Partial Dependency exists, when for a composite primary key, any attribute in the table depends only on a part of the primary key and not on the complete primary key.
• To remove Partial dependency, we can divide the table, remove the attribute which is causing partial dependency, and move it to some other table where it fits in well.

Third Normal Form (3NF)

• It is in the Second Normal form.
• And, it doesn't have Transitive Dependency.

Boyce and Codd Normal Form (BCNF)

Boyce and Codd Normal Form is a higher version of the Third Normal form. This form deals with certain type of anomaly that is not handled by 3NF. A 3NF table which does not have multiple overlapping candidate keys is said to be in BCNF. For a table to be in BCNF, following conditions must be satisfied:

• R must be in 3rd Normal Form
• and, for each functional dependency ( X → Y ), X should be a super Key.