To build an Oracle DEREF query, follow these steps:
- Identify the table or view that contains the REF column that you want to dereference. Ensure that the table or view has been created with the necessary REF constraints to establish the relationships between the tables.
- Use the REF operator to retrieve a REF value for the row that you want to dereference. This can be done using a SELECT statement that includes the REF operator, for example:
SELECT REF(t) FROM my_table t
WHERE t.id = 123;
- Use the DEREF operator to dereference the REF value and retrieve the associated row or object. This can be done by passing the REF value to the DEREF operator, for example:
SELECT DEREF(ref_col) FROM my_table WHERE id = 123;
If necessary, join the dereferenced row or object with other tables or views to retrieve additional related data.
Note that in order for the DEREF operator to work correctly, the referenced table must have been created with a primary key or unique constraint on the column(s) that are being referenced. Additionally, the column(s) being referenced must be defined with the NOT NULL constraint.
Also, keep in mind that the use of REF and DEREF operators can impact the performance of your queries, especially if you are working with large amounts of data. Therefore, it is important to use them judiciously and optimize your queries as much as possible.
Object-Relational queries are queries which can handle data object features on the existing relational data environment.
REF is one of most important data structures in Object-Relational Databases and can be explained as a logical pointer to define the
link between two tables with a similar function.
There are three ways of writing REF join queries which are: