Read this SQL tutorial to learn when to use SELECT, JOIN, subselects and UNION to access multiple tables with a single statement.

A join combines two or more tables side by side. If you do not specify how to join the tables, you get a Cartesian product. This means that SQL combines each row from the first table with every row ...

So lets say I have 5 databases, all with the same schema, but different data. I want to be able to build reports based on the data in all of those databases. How could I construct a view which ...