Syntax: FROM [[LEFT | INNER] JOIN ] ... The FROM clause indicates the component or components from which to retrieve records. If you name more than one component, you are performing a join. For each table specified, you can optionally specify an alias. * The default join type is //LEFT JOIN//. This join can be indicated by the use of either 'LEFT JOIN' clause or simply ',', hence the following queries are equal: SELECT u.*, p.* FROM User u LEFT JOIN u.Phonenumber SELECT u.*, p.* FROM User u, u.Phonenumber p * //INNER JOIN// produces an intersection between two specified components (that is, each and every record in the first component is joined to each and every record in the second component). So basically //INNER JOIN// can be used when you want to efficiently fetch for example all users which have one or more phonenumbers. SELECT u.*, p.* FROM User u INNER JOIN u.Phonenumber p