SQL is the standard language for making queries in relational database such as SQL Server, Oracle, SQLITE, MYSQL, POSTGRESQL, etc.
SQL processing capabilities.
- Creating, deleting, modifying the structure of a table.
- Define the relationship between two or more tables.
- Insert, delete, update data on table.
- Controlling the database
SQL has three parts
DDL (data definition language)
DDL is a part f SQL which consists these commands like create, drop and alter.
DML (data manipulation language)
Data manipulation language consists commands for retrieving data, manipulating data nad updating data.
DCL (data control language)
This part of sql make database data more secured, it consists commands like Grant, Revoke, etc.
Types of SQL.
Interactive SQL is used to operate directly on database.
Embedded SQL consists of SQL commands put inside programs that are mostly written in some other high language loke C, C++.
Distributed databases/Centralized database
In centralized database system, data resides in one single location.
In distributed database system, database is stored in several computers.
Advantages of distributed databases.
- Make data sharing much easy.
- Distributed control, there is multiple database control
- Reliability and availability: Make data more reliable and available, failure of one site does not effect the availability of data.
- Make faster query processing
Disadvantages of distributed databases
- Increase the cost
- Increase overhead
Client server databases
Clients and servers are two different entities in different machines or on the same machine where client program requests services and the server program responds to client demands.
Advantages of client server database model
- Client workstation provides a low cost and user friendly alternative to mainframe computer.
- Client server database model can be used to develop highly complex database applications.
- A server can provide database services to the variety of clients.
- We can access data over the variety of clients like phone, tablet, computer, laptop, etc.
Database security includes policies framed to protect data in a database.
Security addresses the following issues
- Privacy of certain data
- System related security level
- Database integrity
- Preserving policies of the organization
Database backup and recovery
It is the process of storing copies of data that can be used to protect companies data over the data loss.
When there is data loss for database we can access the data from the database backup.
To handle huge amount of data for the companies, in parallel databases multiple CPUs and storage memory used in parallel, through which we can perform operations in parallel.
Advantages of parallel database
- Make Performance improvement
- High availability
- Proper resource utilization
- Increase Reliability
- Possible scale up