I have a job interview test and they said that the test is SQL queries based on data modeling. What do you think they mean? Will they give me a database diagram and they will ask me questions such as select all rows from tables X and Y where x.salary>y.salary?
Bizarre; I can't imagine what the qs will be. SQL queries and data modeling have nothing to do with each other. [Data models, perhaps, but not data modeling itself.]
That must be it. I guess they are not going to show you actual DDL ("CREATE TABLE ...") but instead just show you a picture. That means your code may not be the very best in some cases, as you won't know for sure the underlying data types of the columns.
Itzik Ben-Gan. Superb T-SQL coder and instructor, particularly on advanced topics. But I believe he has some articles/books on general queries too. If you really want to learn it, I suggest books.