Why SQL Is Important in Testing?

Database is a must for every system. Information (about user or transaction state) is usually maintained in traditional relational databases such as MySQL and Oracle.

SQL is a standard computer language for relational database management and data processing. It allows to query, insert, update and modify data. You can think of SQL as a means of communication between the user and the DBMS (Database Management System).

Simply put, SQL is the programming language which helps to access our database.

To define an SQL query, we first need to understand what is a query. A query can be defined as a request for data from a database via a DBMS. A query can be thought of as an instruction sent to the DBMS to retrieve a dataset based on criteria. Such a query can be developed using SQL and is called an SQL query.

A simple SQL query would be: Select * from Table.

By looking at this query, you can easily understand what does it do — selects all the data (represented by *) from the table.

When you do functional testing of the system through the frontend (website, mobile apps, etc.), you also need to check if the data you are sending is being updated correctly in the database.

The demand for universal testers is growing. This means that testers must be proficient in testing the functionality of a system using traditional testing methods (point-click-and-test) and be able to use technical knowledge to test all aspects of the system. This knowledge includes skills about validation of operating system, interface and database. In this case, we emphasize the importance of good skills in  Structured Query Language (SQL).

Importance of SQL Skills to a Software Tester

Some applications require strong SQL validation skills, some require intermediate skills, and others require no SQL knowledge at all.

Take, for example, websites that host documents that users can send to a printer. Printing these documents requires users to first install a dedicated print controller on their PC. Testing their print quality, in this context, involves printing documents from combinations of various operating systems, browsers and printers. You don’t need to apply any SQL skills for this test. SQL experience is required to validate test data, insert, update and delete test data values ​​in the database.

Let’s take a look at another project —  participating in backend testing which requires a strong knowledge of SQL queries. Internal user interface tool for retrieving data from an Oracle database based on input values. Testing compares the output of the user interface tool and the output of the database, and enters the same values ​​into the tool and the database to ensure that the tool is functioning as expected. Each time the input values ​​change, the database administrator uses a select statement to issue very large queries to the test team. First, you need to understand the relationship between tables, columns and a query before using it. In addition, you need to use different types of SQL statements to validate the test data.

A tester must have the following knowledge of the database and SQL:

• They must be able to recognize different types of databases;
• Be able to connect to the database using different SQL connection clients ;
• Have understanding of the relationships between database tables, keys and indexes;
• Have the ability to write a simple select statement or SQL along with more complex join queries;
• Be able to interpret more complex queries.

Most used SQL statements in testing:

• Data Manipulation Language (DML): allows to manipulate data a database. Examples: SELECT, UPDATE and INSERT statements.
• Data Definition Language (DDL): allows to create and modify database objects. Examples: CREATE, ALTER and DROP statements.
• Transactional Control Language (TCL): Manages various transactions that take place in the database. Examples: COMMIT and ROLLBACK statements.
• Inner Join: Retrieves matched records from both tables.
• Distinct: Extracts different values ​​from one or more fields.
• In: this statement is used to find a value in a list or not.
• Between: This operator is used to get values ​​in a range.
• WHERE: specifies which rows to get.
• Like: This statement is used to perform pattern matching; it is used with WHERE statement.
• Order By Clause: specifies the order in which rows are returned, sorts the table records in ascending or descending order. By default, the order is ascending.
• GROUP BY: groups rows that have a common property so that an aggregate function can be applied to each group.
• HAVING: Selects from the groups defined by the GROUP BY statement.
• Aggregate Functions: does calculation involving a range of values ​​and returns a single value. Example: Avg, Min, Max, Sum, count, etc.

SQL is very important in software testing because:

• Validation helps to understand if the data that is added to the form (on the frontend) is being added to the backend or not. For example, when registering a user on the website, some fields are missing, therefore, we see some kind of error message regarding user registration. Also, if we execute the SQL query, we can say that the following fields are missing and there is an error in the user registration function module.
• SQL helps us in getting test data. For example, if you need to check some fixes for products that are visible on a working website. Using an SQL query, you can get products with a specific condition (filtering) and change the product description for all records at the same time.
• SQL helps us in test automation. For example, if we need to make sure that the VIP flag is displayed for a paid registered user after logging in. With the help of SQL we can get the user directly from the database with the specific conditions and then log in using the data and just check the presence or absence of the VIP flag, rather than creating a brand new user and so paying on his behalf.

Given the benefits of working with SQL and the usefulness of SQL skills in general, our advice to testers is — in order to become a versatile tester that is appreciated by customers and companies, you should acquire a minimal knowledge of SQL.