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

When you execute a query using the LEFT JOIN syntax, SQL does two things: It returns all of the records from both tables that contain matching values, as defined by the ON clause.

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 ...

When multiple tables, views, or query-expressions are listed in the FROM clause, they are processed to form one table. The resulting table contains data from each contributing table. These queries are ...