Relational database: The principle of relational pattern design

Relational database: The principle of relational pattern design

1. Paradigm and redundancy of data
From 0NF to 1NF, 2NF, 3NF, BCNF, 4NF, 5NF?
The process of database design is a split table, the purpose of the split is to reduce the data redundancy.

the lower the redundancy of the data, the shorter the transaction duration (it does not require additional operations to maintain data consistency and integrity).
at the same time, the finer the split, the higher the cost of the query (requiring more time-consuming connection operations).

2. Design principles for relational models

if the table (set) is primarily used for data update (Online), the decomposition of the table should be as close to 3NF as possible.

BCNF from the previous example is not necessary, as for the 4NF, 5NF more belongs to the theoretical research field, in the actual should

It is not necessary in use.

If the table (set) is mainly used for data query (statistics, analysis), the decomposition of the table to 1NF, 2NF can be.

for frequently used queries, You can even use data persistence technology,

provides support for data queries with specialized tables (sets) .

excerpt from:http://www.cnblogs.com/huangcongcong/p/4004779.html

Relational database: The principle of relational pattern design