Video Tutorial 2 SQL. Types of Databases, SQL Clients and Schemas.

In this tutorial we are going to talk about different types of databases, different types of SQL clients and the definition of SCHEMA.


A collection of information organized in such a way that a computer program can quickly select desired pieces of data.

Traditional databases are organized by fields, records and files. A field is a single piece of information; a record is one complete set of fields; and a file is a collection of records. For example, a telephone book is analogous to a file. It contains a list of records, each of which consists of three fields: name, address, and telephone number.

Types of databases

We can organize databases in several ways; taking into account the information we are organizing or our needs.

We found interesting the distinction between "the commercial databases" and the "open source databases".

Open source databases have the advantage that they are free and that they have a supporting community behind them.

SQL Server

SQL Clients

SQL clients belongs to the software architecture model consisting of two parts, client systems and server systems, which communicate over a computer network or on the same computer. A client-server application is a distributed system consisting of both client and server software. The client process always initiates a connection to the server, while the server process always waits for requests from any client.

There are two different types of SQL clients;

  1. The ones in which we directly write the SQL statements:
    • Command-line interface
  2. The ones which write SQL statements for us;
    • Graphic client; for example MySQL workbench.
    • A program; if we are working with JAVA, we will use a JDBC API.

Database Squema

A database schema of a database system is its structure described in a formal language supported by the database management system (DBMS) and refers to the organization of data as a blueprint of how a database is constructed (divided into database tables in case of Relational Databases) .(wikipedia)

Notice that we are going to find the word Squema used in other ways;

  1. XML files; An XML schema is a description of a type of XML document, typically expressed in terms of constraints on the structure and content of documents of that type, above and beyond the basic syntactical constraints imposed by XML itself.
  2. A squema can be used as a graphic for tables and their relations.
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