First Normal Form (1NF)
First normal form (1NF) sets the very basic rules for an organized database:
• Eliminate duplicative columns from the same table.
• Create separate tables for each group of related data and identify each row with a unique column or set of columns (the primary key).
Second Normal Form (2NF)
Second normal form (2NF) further addresses the concept of removing duplicative data:
• Meet all the requirements of the first normal form.
• Remove subsets of data that apply to multiple rows of a table and place them in separate tables.
• Create relationships between these new tables and their predecessors through use of foreign keys.
Third Normal Form (3NF)
Third normal form (3NF) goes one large step further:
• Meet all the requirements of the second normal form.
• Remove columns that are not dependent upon the primary key.
Fourth Normal Form (4NF)
Finally, fourth normal form (4NF) has one additional requirement:
• Meet all the requirements of the third normal form.
• A relation is in 4NF if it has no multi-valued dependencies.
Clustered index vs Non clustered index
ReplyDelete- A table can have only one clustered index, 249 non clustered indexes
- "primary key" is the ideal column for a clustered index."Unique Key" is the ideal column for a nonclustered index
- Dictionary is example of clustered index, Text book is an example of non clustered
- The clustered index is SORTED, and the nonclustered index is UNSORTED
- Clustered indexes are good for range searches. Non-clustered indexes are good for random searches.