How the SQL language works and why it is so in demand

Developed by Oracle in 1979, SQL was initially a simple tool for searching for specific data, similar to filters in Excel. Over time, it has become more sophisticated and is now considered a key tool for data processing. With SQL, you can:

• — create and store data in the form of tables;
• – change the content and structure of these tables;
• – combine different data sets and perform calculations;
• — manage security and control access to information.

For example, a large company has 500 employees. 100 of them are in sales and use the CRM system to enter data on clients, transactions, and amounts. Another 15 IT specialists configure and update the system. And 20 accountants regularly download information on payments, invoices, and documents. Using SQL, you can grant each employee access to only the portion of data they need, protecting sensitive information and maintaining the integrity of the system.

• It’s a query language, not a programming language. It’s used in addition to Python, JavaScript, or C++, but only for working with databases. It’s impossible to write a full-fledged website or application in it.
• A clear and understandable structure makes the SQL language for working with data relatively easy for beginners.
• Universality. There are unified standards for constructing queries across all databases and browsers, allowing for the processing of even very large volumes of information.
• Shared access. SQL allows you to create interactive queries. This means you can access the data you need online and make decisions based on it.
• Access management. Using SQL, you can grant, deny, or restrict access to data for different user groups, as well as assign them specific functions: read, modify, create, delete, and copy. This protects databases from hacking or unauthorized changes.

SQL is used by Facebook, Google, Amazon, Uber, Netflix, and Airbnb. For example, to show users personalized recommendations based on what they watch, read, and like.

SQL is essential for developers, testers, data analysts, administrators, and marketers—anyone whose job requires downloading and processing large volumes of data. Properly structured queries help extract useful information about clients and users, sort it into specific categories, and analyze website or business performance.

For example, an online store delivers goods nationwide and has a large customer base. The store owner wants to understand how to improve delivery and which regions to focus on. To do this, they assign a task to an analyst who, using SQL queries, extracts data for each region and sorts it by order volume.

A database is a way of storing and organizing data that is structured so that it can be used by both humans and algorithms.

SQL allows you to work with relational databases—those where data is presented in tables. This is somewhat similar to tables in Excel, but all tables within a single database are linked via end-to-end search.

The structure of an SQL database consists of six elements:

• The key is the most important column that links the data tables.

They are:

• — primary — contain a unique identifier for each object, for example, an article number;
• — potential — contain an alternative identifier;
• — external — contains a link that allows you to link two tables, where the key values ​​in one table correspond to the primary key in the other.

• A relation is a table with data presented in rows and columns.
• An attribute is a column that contains a name, type, price, or other parameter.
• Domain – the values ​​that are valid for this attribute: for example, the price in rubles or the name in Cyrillic characters.
• A tuple is a numbered string that contains all the data about an object.
• Value is the content of a cell in a table.

To work with databases using SQL, a database management system (DBMS) is used—an intermediary between the user and the server where the tables are stored. DBMSs are a suite of software that allows you to create and manage databases.

DBMS can be free or commercial, for example, MySQL, Microsoft SQL Server, SQLite, Oracle, and Ingres.

When a user makes a query to a table with data, it looks like this step by step:

1. A client is an interface used to create a query. For example, the Google search bar.
2. DBMS (database management system) is responsible for transmitting a request from the user to the database and returning a response in a form that is understandable to the user.
3. A database is tables where data is structured and linked to each other so that you can quickly find what you need.

To perform all these operations, the system uses the SQL database language. This is done using special commands called operators.

Here are the main types of SQL statements:

• DDL (Data Definition Language) — data definition statements that operate on entire tables. For example: CREATE — to create a table (TABLE) or database (DATABASE), DROP (TABLE/DATABASE) — to delete an entire table or database, USE — to select the desired database.
• DML (Data Manipulation Language) — data manipulation operators that work with table contents. For example, UPDATE — to update data, DELETE — to delete, INSERT — to add new data, SELECT (FROM/WHERE) — to select the desired data based on a specified parameter.
• DCL (Data Control Language) is an operator used to define data access for different users. For example, GRANT to allow access or DENY to deny access.
• SQL client-server – for managing access to data for different users.
• Three-tier SQL architecture – to protect data from unauthorized copying and distribution.

In addition to operators, TCL (Transaction Control Language) is used —a language for managing transactions, that is, a series of commands that are executed sequentially. If even one command fails, all subsequent commands are also canceled. This happens, for example, with online payments, when data must be entered and confirmed sequentially. For example, BEGIN TRANSACTION begins a transaction, COMMIT TRANSACTION modifies commands in a chain, and SAVE TRANSACTION is an intermediate save point within a transaction. 

Step 1: Watch educational videos and read books on the topic.

For example, “SQL: A Complete Guide,” “SQL Database Programming: Common Errors and How to Fix Them,” or “Introduction to Database Systems.” These will help you understand the theory behind how databases and DBMSs work, how to write queries, and how to create tables.

Step 2: Get familiar with the most popular DBMS.

The main ones are Oracle, MySQL, PostgreSQL, and Microsoft SQL Server. Books, videos, and online courses can help you understand the features and differences between each DBMS and which one to choose.

Step 3: Try your hand at online training.

This will help you get the hang of the simplest commands and then move on to more complex exercises or even a real DBMS.

Using the online simulator in the “SQL for Working with Data and Analytics” course, you can practice writing simple or more complex queries.

The courses provide systematized knowledge that can be immediately applied in practice.

For example, the “SQL for Data Science and Analytics” course is suitable for both those already familiar with SQL or Python and those who want to learn it from scratch to apply it to work-related tasks, product analytics, and marketing research. It will help you master the necessary skills in six weeks. The training is designed so that you can immediately put the acquired knowledge into practice and understand its purpose.

• The SQL query language is used to work with large databases with uniquely structured information. It helps you quickly extract the required data and filter it by dozens of different parameters.
• SQL and DBMS are used by major IT companies, online stores, and services that require quickly displaying information in response to millions of queries. These include Netflix, Google, Microsoft, and Amazon. Therefore, specialists proficient in SQL are in high demand.
• Learning the basics of the SQL query language will be easier for those who are already familiar with formulas in Excel spreadsheets.
• Knowledge of the SQL language will be useful for data analysts, marketers, product managers, and financial specialists.

SQL is an essential skill for working with data, and you can learn it for free. Our course will help you understand the basics of the query language: you’ll learn how to manage data, solve practical problems, and gain valuable experience in an interactive simulator.