Why do we need SQL language in testing?

Indeed, in the modern world, storing large volumes of data on paper is neither convenient nor efficient. This is why databases were invented, wherein substantial amounts of information are stored, organized, and exchanged.

Key Concepts

SQL (Structured Query Language) is the standardized programming language for relational databases. In other words, it's the language we use to interact with databases.

A Relational Database is a database represented in a tabular form where data can be accessed and retrieved in various ways without reorganizing the database.

This solution was introduced in 1970 and was initially known as SEQUEL (Structured English Query Language), but the name was later shortened to SQL. Oracle was the first company to offer such a system for managing relational databases.

With SQL, you can:

• execute queries;
• update and reorganize data;
• create and modify the structure of a database;
• manage data access.

Examples of database management systems are:

• MS SQL Server;
• MySQL;
• MS Access.

Let's take a simple example of a data table:

Here are examples of the SELECT and INSERT queries in SQL:

SELECT NAME FROM STUDENTS WHERE AGE = 18; 

The selection of students aged 18 years

INSERT INTO STUDENTS (ID, NAME, AGE, COUNTRY, GENDER) VALUES (7, "NICK", 20, "USA", "MALE")

VALUES (7, “NICK”, 20, “USA”, “MALE”)

This way we add the seventh student to the table

SQL Skills in Tester's Work:

Since nearly every Internet program uses SQL for both database creation and querying, testers must understand how the technology works. This significantly improves the product testing process.

SQL knowledge is useful for:

• writing simple and complex SQL queries;
• understanding the relationship between tables;
• connecting to databases;
• recognizing different types of databases.

Let's consider cases where SQL skills are less needed in testing:

• testing a program from an end-user perspective (black-box testing);
• testing applications where the main focus is on user interface, usability, and accessibility;
• cross-browser testing.

Obviously, in projects requiring database updates, migrations, or data upgrades, SQL knowledge is essential.

An example of a situation where a tester uses SQL:

A tester queries the database to retrieve data that corresponds to a specific filter. Then, in the application that uses this database, they test the filtering function with the same filter. This allows you to compare whether the application correctly displays all necessary elements.

Key SQL Operators for Testing

1. SELECT – the most important operator for database testing. It retrieves data rows from one or more tables that satisfy a given set of criteria. 
2. DML (Data Manipulation Language) – data manipulation operators including INSERT, UPDATE, and DELETE. 
3. DDL (Data Definition Language) – operators for managing test tables, including CREATE TABLE, ALTER TABLE, and DROP TABLE. 
4. TCL (Transaction Control Language) – operators for managing database transactions, including COMMIT and ROLLBACK. 
5. Inner Join – operator for getting corresponding records from both tables. 
6. Distinct – operator for retrieving distinct values from one or more fields. 
7. In – operator for finding a value in a list. 
8. Between – this operator retrieves values within a specific range. 
9. Order By Clause – managing data in ascending or descending order. 
10. GROUP BY – groups rows sharing a common property to apply an aggregate function to each group. 
11. HAVING – selects from groups defined by the GROUP BY operator.

Aggregate functions: perform calculations with a range of values and return a single value. Example: Avg, Min, Max, Sum, Count, etc.

The profession of a QA is becoming more and more popular, so for successful employment, traditional testing methods such as «click and check» are not enough. Knowledge of SQL basics is one of the ways to increase your competitiveness in the QA market and is becoming an increasingly common requirement for recruiters when looking for candidates. That's why it's important to know and understand SQL basics and be familiar with key operators.