1, the concept of the database
The database is stored together in a certain way, can be shared with multiple users, with as little redundancy, and application data set independently of each other, can be regarded as electronic file cabinets - premises storage of electronic documents, users can add the data file, query, update, or delete operation.
(1) relational database
Relational database storage format can directly reflect the relationship between the entities. Relational databases and common form is quite similar to relational database tables between the table and there is a lot of complex relationships. Common relational databases have Mysql, SqlServer and so on. In the lightweight or small applications, using a different relational database has little effect on system performance, but when building large applications, you need to business needs and performance requirements of the application in accordance with, select the appropriate relational database.
(2) non-relational databases
With the recent expansion of the technical direction, a large number of databases such as NoSql MongoDB, Redis, Memcache database structure for simplicity, to avoid redundancy, the connection table affect performance, abandon complex distributed object is designed.