Oracle UDT References over DBLINK: A Comprehensive Guide
In the world of database management, the use of user-defined types (UDTs) has become increasingly popular. These custom data types allow for more flexibility and efficiency in storing and retrieving data. However, when it comes to UDT references over database links (DBLINK), there are some important considerations to keep in mind. In this article, we will explore the ins and outs of using UDT references over DBLINK in Oracle databases.
First, let's start with a brief overview of what UDTs and DBLINKs are. UDTs are user-defined data types that are created by the user, rather than being predefined by the database system. They can be used to store complex data structures, such as arrays, nested tables, and objects. DBLINKs, on the other hand, are database objects that allow for communication between two databases. They enable users to access and manipulate data from a remote database as if it were local.
Now, let's dive into how UDT references work over DBLINKs. When referencing a UDT over a DBLINK, the syntax is similar to referencing a regular table. However, there are a few key differences. The first difference is that you must specify the owner of the UDT in the reference, followed by the name of the UDT. For example, if the owner of the UDT is "HR" and the UDT is named "EMPLOYEE_TYPE", the reference would be "HR.EMPLOYEE_TYPE@DBLINK_NAME". This is important to note because when creating a UDT, it must be created in the same schema as the table that will be using it.
Another important aspect to consider is the use of synonyms. If the UDT is referenced using a synonym, it must be created in the same schema as the synonym, not the schema of the table. In this case, the reference would be "SYNONYM_NAME@DBLINK_NAME". It is also worth noting that the synonym must be created on the local database, not the remote one.
One of the main benefits of using UDT references over DBLINKs is the ability to perform queries and DML operations on remote UDTs. This allows for efficient data manipulation and retrieval from a remote database. However, there are some restrictions to keep in mind. For example, when querying a UDT over a DBLINK, you cannot use the "SELECT *" syntax. Instead, you must explicitly list out the columns you want to retrieve. Additionally, only simple comparisons can be made on UDT attributes, such as equal or not equal. More complex operations, such as greater than or less than, are not supported.
When it comes to data manipulation, DML operations on UDTs over DBLINKs are limited to INSERT, UPDATE, and DELETE statements. However, there are certain restrictions that apply. For example, when updating a UDT over a DBLINK, you must provide values for all attributes, even if you only want to update one. This is because the entire UDT is sent over the DBLINK for the update to be applied. Similarly, when inserting a UDT over a DBLINK, all attributes must be provided with values, including those with default values.
In terms of performance, UDT references over DBLINKs can have some impact. This is due to the fact that the entire UDT is sent over the DBLINK for each query
