MySQL is an open-source RDBMS solution that was purchased by Oracle in 2008. As a component of the popular LAMP web application development stack, MySQL powers some of the world’s most highly visited websites, including Facebook, Twitter, and YouTube.

Microsoft SQL Server (MSSQL) is an RDBMS solution developed and maintained by Microsoft. First released in 1989, SQL Server is now available in many different versions with different feature sets, including Enterprise, Standard, and Express versions.

Used for Whom?

For different situations, the choice is easy which one to choose, like with PHP it's easy to work with a MySQL database. If you are going to start a project with Microsoft Visual Studio and program in ASP.NET then it may be easier to work with an MS-SQL database.

For a WordPress site, a MySQL database is the only choice. Drupal has a small community that does develop to get this on MS-SQL. However, it is recommended to use a MySQL database for this. This causes fewer problems.
It is also a large part personal preference that determines which database you use. If you have always worked with 1, then this will be your preference. MS-SQL has the advantage and disadvantage that it is closed source, the positive side is that the integration with certain programs is effortless. Also, the software package SQL management Studio is available, this is a tool to manage the database. With the 2012 version, it is no longer possible to access this via the web.

Operating System

When selecting an enterprise-grade database, most companies have already invested a great deal of time, money, and expertise in their IT infrastructure—including their choice of operating system. This means that whether you go with MySQL or SQL Server, your choice of database solution needs to mesh well with your existing workflow.

Fortunately, both MySQL and SQL Server run on virtually all major operating systems. MySQL is traditionally associated with Linux as part of the famed LAMP stack (Linux, Apache, MySQL, PHP). However, it also offers full-fledged support for Windows and Mac OS X, as well as other Unix-based operating systems.

SQL Server, meanwhile, is developed by Microsoft and was originally written for Windows. In recent years, however, Microsoft has made strides in embracing the open-source community, which includes providing support for both Linux and Mac OS X. The most recent versions of SQL Server run on Linux natively and will run on Mac OS X within a Docker container.

Pros Cons

Pros of SQL

• SQL makes data retrieval easier by using only basic keywords (SELECT, INSERT, etc.) rather than complex coding.
• The SQL community has around 25K members, with several experts ready to share valuable tips and best practices.
• While SQL databases' standardized schema makes data modification difficult, it benefits data integrity, consistency, confidentiality, and compliance.
• SQL databases are ACID compatible due to the highly structured form of relational database tables. This degree of compliance brings tables in sync and ensures transactional validity.

Cons of SQL

• Some SQL versions have a high operational cost, making it difficult for some programmers to use them.
• Sometimes SQL programmers might not have complete control over the database because of the underlying business rules.
• SQLs hardware requirements include routine maintenance and operational charges, making it expensive to use.
• The SQL interface is complicated, making it difficult for certain users to adopt.

Pros of using MySQL

• It allows easy installation in a package manager-enabled operating system. Your MySQL will be ready with just a single command-line installation.
• Although Oracle owns MySQL, the software remains open-source and free to use. Since everyone can access the source code of MySQL, it is less expensive and safer to use.
• MySQL doesn't use much of your computer's memory or CPU. Therefore it doesn't cost  much in terms of resources.
• MySQL will not be outdated for a long time. Its customer base continues to grow, new features are added, and its performance and security keep improving.

Cons of using MySQL

• When it comes to writing stored procedures and triggers, MySQL provides fewer options than other feature-rich RDBMS such as Postgresql.
• It can only be set up as a server database, so you can't use it in a portable app. It is not suitable for embedded systems.
• MySQL is not scalable. It needs a significant amount of effort to make it extensible, so many users are turning to MongoDB these days.

• MySQL does not support relatively huge database sizes. MySQL performs well in most small and medium-sized applications, but its performance degrades as data size expands.

Server Performance

Database performance holds a significant value for any software application. The entire system slows down if your database doesn't respond quickly and efficiently, generating undesirable delays for the end-user. User experience and revenue are affected negatively by poor database performance.

Both MySQL and SQL Server provide equivalent speed and efficiency for high-end applications. They are highly capable of supporting several databases on a single server.

However, SQL Server outperforms MySQL in many SELECT, INSERT, UPDATE, and DELETE queries. Also, SQL Server performs better than MySQL in terms of response time. MySQL exhibits a two-fold increase in time as the number of rows grows when scaling. Although SQL Server shows an increase in time, it is not as significant as MySQL. As a result, SQL Server beats MySQL even in terms of scalability.

So, now you know the key differences between MySQL and SQL Server. But, theoretical knowledge might sometimes fade away over time. Therefore, you need to gain some practical knowledge as well.