Database Normalization: 2nd Normal Form (Reducing Redundancy based or partial functional dependence) 

In this video we discuss normalization at the level of "Second Normal Form". When we moved to First Normal Form by flattening the file to eliminate an multi-valued fields, we typically introduced some redundancy. If we resist (for now) the temptation to introduce an overall primary key for the table, we might have a composite primary key -- a combination of fields which as a team uniquely identify each row of the table. Field B is "functionally dependent" on Field A if knowing Field A means that we can determine (maybe just by looking something up) Field B. To arrive at Second Normal Form, we split up a table into multiple tables by taking at properties (fields) that depend on only a part of the composite key into a separate table. It must remain possible that a JOIN query would reproduce the original table.