I have a gut feeling that I will retake a test about these subjects. Do you know good resources about creating ER diagram and relational model for database (sql database primarily) Sometimes even creating a correct ER Diagram (chen notation) feels difficult and confusing. These type of homework problems have been things like word problems where we must construvt the ER diagram from a short written description. For relational model... I think I can create relational model when I have the correctly defined ER diagram from which to begin work... I think I could also use some resources for SQL queries but I do know already some basic queries. I studied some basic queries at w3school and I took the quiz about SQL but still I dont really have good enough understanding for a test at our school. But I dont quite fully understand the logic begind the queries. Especially Left join, right join, aliases, inner join, And the logic begind the where operator in SQL queries is a little bit fuzzy to me. Especially if you somehow combine multiple tables in a query. How are you supposed to know which fields(?) Are equal to which fields in lets say two tables...?