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SQL/MySQL RDBMS Concepts



Objectives

in this section, we have seen about RDBMS(Relational Database Management System) in SQL/MySQL

What is RDBMS?

RDBMS(Relational Database Management System). RDBMS is the basis for SQL and for all modern database systems like MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access. a relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational models. It uses a structure that allows us to identify and access data in relation to another piece of data in the database. Often, data in a relational database is organized into tables. a table is the most common and simple form of data storage in a relational database. the concept of the table we have to see in next point.

Example of Table Relational Database:-

root@cyberdevil:~# mysql -u root -p
Enter password: 
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 51
Server version: 10.3.20-MariaDB-1 Debian buildd-unstable

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| TutorialBoy        |
| information_schema |
| mysql              |
| performance_schema |
+--------------------+
4 rows in set (0.001 sec)

MariaDB [(none)]> use TutorialBoy;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
MariaDB [TutorialBoy]> show tables;
+-----------------------+
| Tables_in_TutorialBoy  |
+-----------------------+
| users                 |
+-----------------------+
1 row in set (0.000 sec)
 
MariaDB [TutorialBoy]> select * from users;
+----------+--------------+----------+
| username | email        | password |
+----------+--------------+----------+
| omkar    | ac@gmail.com | abc      |
| abc      | yz@gmail.com | xyz      |
| parthe   | op@gmail.com | pass     |
+----------+--------------+----------+
3 rows in set (0.000 sec)

MariaDB [TutorialBoy]>


What is Table?

The data in RDBMS is stored in database objects called tables. The table is a collection of related data entries and consists of columns and rows. Relational database model, a table is a collection of data elements organized in terms of rows and columns. A table is also considered a convenient representation of relations. But a table can have a duplicate row of data while a true relation cannot have duplicate data. The table is the simplest form of data storage. Below is an example of an Employee table.

Example :

MariaDB [TutorialBoy]> select * from users;
+----------+--------------+----------+
| username | email        | password |
+----------+--------------+----------+
| omkar    | ac@gmail.com | abc      |
| abc      | yz@gmail.com | xyz      |
| parthe   | op@gmail.com | pass     |
+----------+--------------+----------+
3 rows in set (0.000 sec)

What is the field?

A table consists of several records(row), each record can be broken into several smaller entities known as Fields. Every table is broken up into smaller entities called fields. The fields in the USERS table consist of NAME, EMAIL, and PASSWORD. a field is a column in a table is designed to maintain specific information about every record in the table.

Example :

MariaDB [TutorialBoy]> select * from users;
+----------+--------------+----------+
| username | email        | password |
+----------+--------------+----------+
| omkar    | ac@gmail.com | abc      |
| abc      | yz@gmail.com | xyz      |
| parthe   | op@gmail.com | pass     |
+----------+--------------+----------+
3 rows in set (0.000 sec)

In the above example, the different fields are highlighted with different colors.

What is a record/row?

A record is also called a row of data. is each individual entity that exists in a table. for example, there are 3 records in the following USERS table.

Example :

MariaDB [TutorialBoy]> select * from users;
+----------+--------------+----------+
| username | email        | password |
+----------+--------------+----------+
| omkar    | ac@gmail.com | abc      |
| abc      | yz@gmail.com | xyz      |
| parthe   | op@gmail.com | pass     |
+----------+--------------+----------+
3 rows in set (0.000 sec)


What is a Column?

A Column is a vertical entity in a table that contains all associated with a specific field in the table. in the Relational table, a column is a set of values of a particular type. The term Attribute is also used to represent a column. in the following example the username, email, the password is a column.

Example :

MariaDB [TutorialBoy]> select * from users;
+----------+--------------+----------+
| username | email        | password |
+----------+--------------+----------+
| omkar    | ac@gmail.com | abc      |
| abc      | yz@gmail.com | xyz      |
| parthe   | op@gmail.com | pass     |
+----------+--------------+----------+
3 rows in set (0.000 sec)


What is a NULL value?

A NULL value in a table is a value in a field that appears to be blank, which means a field with NULL values is a field with no value. it is very important to understand that NULL value is different than zero value or a field that contains spaces. A field with NULL values is one that has been left blank during record creation.

Example :

MariaDB [TutorialBoy]> insert into users(email,password) values ('tb@gmail.com','123');
Query OK, 1 row affected (0.336 sec)

MariaDB [TutorialBoy]> select * from users;
+----------+--------------+----------+
| username | email        | password |
+----------+--------------+----------+
| omkar    | ac@gmail.com | abc      |
| abc      | yz@gmail.com | xyz      |
| parthe   | op@gmail.com | pass     |
| NULL     | cw@gmail.com | 123      |
+----------+--------------+----------+
4 rows in set (0.000 sec)



In the above example, the data has been inserted in only two fields EMAIL and PASSWORD and the USERNAME field is treated as a NULL value.

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