What is SQL?
1. Introduction: What does SQL stand for?
SQL stands for Structured Query Language. It’s the standard language used to interact with relational databases — that is, databases that organise data into tables (rows and columns) and define relationships between them.
Using SQL, you can store, retrieve, update, and delete data in an organised way.
2. Why is SQL important?
- Many applications — websites, business systems, mobile apps — rely on back-end databases that hold user records, transactions, logs, etc.
- As a QA or automation tester, knowing SQL helps you verify that what the UI shows is actually stored correctly in the database.
- SQL is a highly transferable skill: once you know it, you can work with many different database systems (MySQL, PostgreSQL, SQL Server, Oracle) because they all support SQL in one form or another.
- SQL is declarative: you state what data you want, not always how to fetch it. The database engine decides the optimal retrieval path.
3.How does SQL fit into the database world?
In a relational database:
- Data is organised into tables. Each table has columns (fields) and rows (records).
- Tables may be linked by keys (for example, a “customer” table might link to an “orders” table via a customer ID).
- SQL is the language used to operate on these tables: to query data, define table structures, and manage access rights.
For example, imagine a table Orders:
| OrderID | CustomerID | OrderDate | TotalAmount |
| 1001 | 200 | 2025-11-14 | 349.50 |
| 1002 | 201 | 2025-11-12 | 129.99 |
You could use SQL to ask: “Show me all orders where TotalAmount is over 300.”
SELECT OrderID, CustomerID, TotalAmount
FROM Orders
WHERE TotalAmount > 300;4.Basic types of SQL commands
SQL is often categorised into several sub-languages:
- DDL (Data Definition Language) – commands like CREATE, ALTER, DROP which define or modify the database structure.
- DML (Data Manipulation Language) – commands like INSERT, UPDATE, DELETE which modify the actual data.
- DQL (Data Query Language) – primarily the SELECT statement, used to retrieve data.
- DCL / TCL – commands for permissions (GRANT, REVOKE) or transaction control (COMMIT, ROLLBACK).
5. A quick, practical example
Let’s create a simple “Employees” table (for demonstration) and then query it.
CREATE TABLE Employees (
EmployeeID INT PRIMARY KEY,
FirstName VARCHAR(50),
LastName VARCHAR(50),
City VARCHAR(50),
Salary DECIMAL(10,2)
);Insert some data:
INSERT INTO Employees (EmployeeID, FirstName, LastName, City, Salary)
VALUES (1, 'Vinoth', 'Rathinam ', 'London', 55000.00),
(2, 'Carl', 'Wilson', 'Manchester', 47000.00),
(3, 'David', 'Jeff', 'Bristol', 62000.00);Now a query:
SELECT FirstName, LastName, Salary
FROM Employees
WHERE Salary > 50000
ORDER BY Salary DESC;Result:
| FirstName | LastName | Salary |
| David | Jeff | 62000.00 |
| Vinoth | Rathinam | 55000.00 |
This example illustrates how you:
- Create a table (DDL)
- Insert data (DML)
- Retrieve data using SELECT, a WHERE condition, and ORDER BY (DQL/DML)
6. Summary
In simple terms:
- SQL is your tool for interacting with relational databases.
- It allows you to query and manipulate structured data.
- For testers and automation engineers, mastering SQL means better verification of backend data, improved ability to generate test datasets, and deeper understanding of how applications persist data.
