Before dwelling into Referential Join, understanding the foundation i.e., Referential Integrity is very important. The existence of the relationship between two tables based on the presence of the primary key of the parent table is necessary to have the referential integrity between the two tables.
Consider the MARA table where material number is the key. Any relationship between ZTable ABC and MARA would have referential integrity only if the foreign key material number in ABC exists in the primary key material number in MARA. Hence, there cannot be a material number in ABC that is not a valid value in MARA.
Referential Join is a join between two tables, which ensures that referential integrity is always maintained between the tables in question. Any record on the left will have a corresponding record on the right if the table on the right is taken into consideration. This means, if the fields from both the table are considered in the query, the referential join will act like inner join. Otherwise, if the fields from the right table are not considered, it will act as a left outer join.
In HANA, Referential Join is available in Attribute and Analytic views. Referential Join is not available in Calculation view.