The Flow of Information

First of all you have to understand the procedure of the flow of information between you as a user and the database when you are using SQL.

This flow of information consists of commands as well as data and is always handled by the DBMS which undertakes to manage them. All communications between the user and the database is made by the DBMS. Users requests are sent to the DBMS and after proper processing they are turned into a readable and writeable format to the database engine. The procedure below shows the path of processing that an SQL command follows: • SQL request DBMS processes and sends a request to the Database Engine. • Database Engine retrieves data from database and returns the result to DBMS which returns data to user. The tables keep the data of the database and control its structure. Through the DBMS you must be able to submit queries to database for the values of its tables in order to see, to change, to delete or to add new data to them.  Thus, the SQL92 standard SQL language implementation offers more than 40 commands in connection with all DBMS functions such us data access control, data definitions, data retrieval, data handling, data sharing and data integrity. In order to cover weaknesses of SQL in connection with the flow control and conditional statements we use other programming languages like C, PHP or Pascal working in a joined very powerful programming environment as we will see in detail later.