SQL

 SQL- Structured Query language.

·          It is programming Language (Query Language),it is designed for managing data held in a relational database management system.

Database- organized collection of structured information, or data.

DBMS

A database management system (DBMS) is system software for creating and managing databases.
A DBMS makes it possible for end users to create, protect, read, update and delete data in a database.

1) Hierarchical DBMS
model data is organized in a tree-like structure. Data is Stored Hierarchically (top-down or bottom-up) format.
Data is represented using a parent-child relationship.
 
2) Network Model
It will helps you to address the need to model more complex relationships.

many-to-many relationship example - orders/parts.
In this model, entities are organized in a graph which can be accessed through several paths.
Relational Model

3) Relational DBMS is the most widely used DBMS model because it is one of the simple one.
This model is based on normalizing data in the rows and columns of the tables. 

Relational model stored in fixed structures and manipulated (Insert/Update/ Delete ) using SQL language.

RDBMS stores data in tabular form.

Data is stored in the form of tables which are related to each other.

Popular RDBMS systems are

Microsoft SQL SERVER

ORACLE
MY SQL

4) Object-oriented Model data is stored in the form of objects.
The structure is called classes which display data within it. 

PostgreSQL

In which Job Roles SQL is important?

Below are Database field related Job Roles- here SQL is the fundamental aspect.

SQL Developer
Database Developer 
Database Engineer
DBA- Database Administrator
Data Scientist
Data Analyst
ETL Developer
Data Engineer