Database and database management systems (1)
Database (DB) stored in the computer is set up according to a certain format of certain data. The operating system does not directly manage them, but to manage them through the database management system (DBMS).
There are many different database management systems, in accordance with the different ways to prevent data to divide. The most common is a relational database (RDBMS), there are many non-relational database. For example key-value storage systems, object-oriented databases.
For RDBMS, the data is organized like a picture of the two-dimensional data table. Wherein the columns are called fields, the row is called a record. A database is a collection of some of the data tables, and management systems for their management.
Where the client using SQL to access the database, the database management system to return data based on SQL. Relational database returns the format of the data must be data sheet, except in the case of error under.
Database using the formula C / S structure, sometimes the client and server can be installed on the same machine, and sometimes may be accessed over a network mounted on a different machine. A database can be connected to a plurality of clients. And the client and database management systems do not necessarily have the same software, in many different languages provide database access interface.
For the language of communication with the client database management system, SQL can be divided into three categories according to the role.
- Create or delete database tables and DDL
- Operating data query or DML
- To confirm or cancel the operation DCL
In fact the most used query data DML .