DB2 and SQL Server are two types of Relational Database Management System. Both come in handy when you have a lot of data to handle your system. The first difference between DB2 and SQL server is that DB2 is from IBM, while SQL is from Microsoft.
Another thing about DB2 is that it can be used on Windows, Linux and Unix server, plus it can only work for computer with high capacity, which means it does not support lower-end computers. SQL server, on the other hand, supports both high-end computers and lower end computers. SQL server generally has some features that will enable you to maintain and run your database. Also, GUI tools are available for you as a developer when you use SQL server. Although DB2 is also equipped with GUI tools, its application and usage are very limited. Finally, SQL server has an inbuilt word indexer, but DB2 does not have.