Third Normal Form (3NF)
Non-PK : Non-PK Relationship (PK=Primary Key)
There should be no dependency among non-key attributes.
Non-key attributes should depend only on primary key(PK) and on no other column. That is, every nonkey attribute should be non-transitively dependent on the primary key.
Third normal form is violated when a non-key column is a fact about another non-key column.
A table is in third normal form if the nonkey attributes that do not contribute to a description of the primary key are move into a separate table, like, for example, look-up tables.
In other words, a record is in second and third normal forms if every column is either (a)part of the primary key, or (b)provides a fact about the whole primary-key (and not its part, if it is a composite key).
As seen from the example above, 3 NF practically means:
§ If a non-key column is dependent upon another non-key column, it logically belongs not to the table it is in, but to a separate table. Hence, spin it off into a separate table.
§ Relate the split table with a foreign key.
Fourth Normal Form (4NF)
Fourth Normal Form (4NF) deals with multi-valued attributes. 2NF, 3NF, BCNF are concerned with functional dependencies, while 4NF and 5 NF are concerned with multi-valued dependency.
4NF disallows more than one independent multi-valued column. That is, there can NOT be more than one (a)independent (b)multi-valued column in a table. To be in Fourth Normal Form, a relation must first be in Boyce-Codd Normal Form. Additionally, a given relation may not contain more than one multi-valued dependency.
Union, Intersect and Minus are set operators that operate between two sets, that is, between result sets of two SQLs, and determine what would be the combined result set of the two.
The number of columns/expressions in the SELECT of the component queries must match, and they should belong same datatype group (char, numeric, ...).