If you want to learn SQL and become a skilled SQL developer, then you should start by learning the basics of the language. You can start by learning the syntax of SQL, which is very easy to understand.
Once you know how to write basic queries and functions, then you can go on to other complex topics like joins or constraints. After completing the advanced topics, you can prepare for the interviews through different sources like educational platforms or YouTube.
For your reference, Intellipaat has a dedicated video for SQL Interview preparation which includes best set of SQL interview questions and answers picked by professionals that will definitely help you to crack your interview and start a career in this domain.