SQL -Structured Query Language - Normalization - Boyce Codd normal form ( BCNF ) Tutorial

BCNF is more advanced in terms of 3 NF. It can also be called 3.5 NF.

• The table must be in 3 NF.
• Still, there is some redundancy based on functional dependency were ( A ->B), which should be handled by making A a primary key

For example – In 3 NF example (Gender -> Salutation). This means Salutation is functionally dependent on Gender.

Hence to achieve BCNF make gender a primary key in other tables.

In this, we can see that table 3 is functionally dependent on table 1.

This means we can obtain the table 3 data i.e contact_no using the user_id of table 1.

This shows that table 3 is functionally dependent on table 1.

So to achieve BCNF

For example, table 2 doesn’t have any primary key till 3NF, while table 1 and table 2 has already primary key user_id and gender respectively.

Hence we added id as a primary key in table 2.