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Current Topic: 2. Java and Databases
Sub-Topics: 2.1. SQL | 2.2. JDBC | 2.3. Oracle | 2.4. MS SQL Server | 2.5. Data Handling Frameworks | 2.6. Java and Databases Project | 2.7. MySql Database | Test Java And Databases
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Data management is one of the most important fields in Information Technology.

We stored data in files, then in Relational Database Management Systems (RDBMS), then in NoSQL databases with key – value families… And this is not the end of the story, just the beginning.

Why do I think so? The methods above invented by us for our computers. But we, people, use very different mechanisms to store information in our brain and body. We have a long way to discover these mechanisms and apply these discoveries to technology.

This section is about RDBMS, the most mature and often used storage systems.

Relational databases consist of tables. The tables have table records with record columns – data fields. Here is the example of the database with two related tables.

Accounts (left) and User Profile (right) tables

User Profile
LoginFirst NameLast Name

Was it clear so far? Highlight the text in question Or

Both tables have the field Login, which relates these tables. This relationship allows our program to figure out the name of a person who sent her/his personLogin and personPassword.
Our program will send into database this query:
Select FirstName, LastName from UserProfile where UserProfile.Login = personLogin and UserProfile.Login = Accounts.Login and Accounts.password = personPassword;

This query is written in Structured Query Language (SQL). More or less understood by people, it is and clear instructional for relational databases. I made bold the keywords in this query. There is an instruction on what to do: select. There is another instruction, from, which points to the tables. There is a conditional part, which starts with the keyword where to indicate the condition of the selection. Our program will select the name (first and last) from the UserProfile table on the condition that the name is taken from the record with the proper login field. But we also want to make sure that the personLogin and personPassword are present in a record in the Accounts table.

It is perfectly OK to read several times the lines above. You are in the new country of RDBMS, learning the new language, SQL.

There are many database vendors. The vendors manufacture many different databases. Just look at the main brands below.
Leading RDBMS in the commercial sector. Highly tunable, reliable, multi-platform require a well-trained database administrator (DBA).
Microsoft SQL Server
Ease of use, relatively low cost and high performance, runs only on the Windows platforms.
Open source DBMS, blistering performance, runs on numerous operating systems, including most Linux versions. To improve performance, it has a slimmer feature set. It does not support some features of relational databases, particularly in how it processes transactions, a part of LX-50 distribution.
Feature-rich RDBMS of the open source world. SQL standards compliant, runs on a wide variety of operating systems and hardware platforms, a part of RedHat 7.3 distribution. PostgreSQL has Geospatial features. It is especially popular in open source Geographical Information Systems (GIS) projects.

The list can go on and on. With all internal differences, all RDBMS are compliant to a single standard: they must speak SQL.
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