A Simple Query with Relationships (The Java EE 6 Tutorial)

The Java EE 6 Tutorial

SELECT DISTINCT p
FROM Player p, IN(p.teams) t

Data retrieved: All players who belong to a team.
Description: The FROM clause declares two identification variables: p and t. The p variable represents the Player entity, and the t variable represents the related Team entity. The declaration for t references the previously declared p variable. The IN keyword signifies that teams is a collection of related entities. The p.teams expression navigates from a Player to its related Team. The period in the p.teams expression is the navigation operator.

You may also use the JOIN statement to write the same query:
```
SELECT DISTINCT p
FROM Player p JOIN p.teams t
```
This query could also be rewritten as:
```
SELECT DISTINCT p
FROM Player p
WHERE p.team IS NOT EMPTY
```