A database management system provides users the access to a database in order to organize, store, retrieve and change an integrated data collection. Relational database system has become a prominent database management system in these days. SQL is a language used to manage data in relational databases. There are some relational database management systems such as Oracle, Microsoft SQL, Server, PostgreSQL and MySQL.
Database management system has some advantages. One of them is centralization which can avoid unnecessary duplication and establish a comprehensive collection of data which can be shared by individual users. In addition to this, security is another strong point of database management system as data can be controlled and protected appropriately by database administrator.
Relational database
A relational database logically represents the data stored in a database by using 2-dimentional table which contain rows and columns.
A figure below demonstrates an example.
The Number column is defined as the primary key in the table and values in the column is used to identify a row uniquely from others. Therefore, two same numbers (primary keys) can not be exist in the Number column.
Furthermore, information stored in relational databases can be stored separately in multiple tables which are connected by foreign keys each other.
SQL
SQL is a most common database managing language. Typing command in the command line is the way you interact with a database management system.
Query
Querying and getting only specific pieces of the data out of a table is main feature of SQL. SQL queries can be done by using several important commands such as SELECT, FROM and WHERE. SELECT command and FROM command can be used to select field(s) and table(s) which users are interested in respectively. WHERE command allows users to filter the data according to certain criteria.
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