Describe the limitations of (2NF) Second Normal Form
Second Normal Form Limitations
Normalizing a table to 2NF ensures that every column in the table is functionally dependent on the entire primary key.
Nonetheless, there are still a number of problems that can occur with tables in 2NF. Consider the following table:
It is represented in relational notation as:
CD (CDNo, Title, Price, CatNo, CatName, DistID
Note that the CatNo and CatName values are repeated in every record. One problem with this table is that you cannot insert information
about a category (such as YA-8) until there is a CD to put into that category. Another problem is that deleting the record of the last
CD in a category (such as CDNo 103) will delete any record of that category.
To prevent these problems, you can decompose your tables to third normal form, which we will look at in the next module.
Problems with 2NF Relations
Although second normal form eliminates problems from many relations, you will occasionally run into relations that are in second normal form yet still exhibit anomalies. Assume, for example, that each new DVD title that DistributedNetworks carries comes from one distributor and that each distributor has only one warehouse that has only one phone number. The following relation is therefore in second normal form: