Currently we are using check constraints for business rules implementation, but I want to know if we should implement business rules in SQL or in the business logic layer (C#). I have searched on the net and found that check constraints are good to use.
Please let me know if someone knows more detailed information about it. One more thing is that the data can be pumped into my database using a mobile application and also using a web application.
Yes, check constraints are a valid tool for business rules.
But are you sure you need to use check constraints, or use a supporting table with a foreign key relationship? If you find yourself defining similar check constraints in various places - the answer is yes, this should definitely be a supporting table.
Data integrity is key; there's not much value to a system that will allow a person to store something that is not per business rules if the application is circumvented. It also makes life a lot easier if the logic is in the database for situations where the original app is in C# and the higher-ups decided the market needs a Java/Ruby/Python/etc version.