With a LEFT OUTER JOIN construction, the query compares each row of entity A with each row of entity B to find all pairs of rows which have an association and thus satisfy the join-predicate. When the association exists and the join-predicate is satisfied, column values for each matched pair of rows of A and B are combined into a result row. However, in contrast to the INNER JOIN construction, the query will also return rows of entity A which do not match entity B. When columns of entity B are specified, these columns contain a null value for these rows.
The syntax is as following:
LEFT [ OUTER ] JOIN entity_path [ ON <constraint> ]
entity_path Specifies the entity to join and the path from an earlier defined entity in the FROM clause to this entity. The path Crm.Customer/Crm.Customer_Address/Crm.Address defines a path from the earlier defined entity Crm.Customer to the new entity Crm.Address.
Constrains the specified entity in the JOIN component of the FROM clause. The constraint syntax is similar as those of the WHERE clause. Only the entities and from-aliases from the current JOIN element and each previous one can be used in the constraint.