Nicknames and data source objects
A nickname is an identifier that you use to identify the data source object that you want to access. The object that a nickname identifies is referred to as adata source object.
A nickname is not an alternative name for a data source object in the same way that an alias is an alternative name. A nickname is the pointer by which the federated server references the object. Nicknames are typically defined with the CREATE NICKNAME statement along with specific nickname column options and nickname options.
When a client application or a user submits a distributed request to the federated server, the request does not need to specify the data sources. Instead, the request references the data source objects by their nicknames. The nicknames are mapped to specific objects at the data source. These mappings eliminate the need to qualify the nicknames by data source names. The location of the data source objects is transparent to the client application or the user.
Suppose that you define the nickname DEPT to represent an Informix® database table called NFX1.PERSON. The statement SELECT * FROM DEPT is allowed from the federated server. However, the statement SELECT * FROM NFX1.PERSON is not allowed from the federated server (except in a pass-through session) unless there is a local table on the federated server namedNFX1.PERSON.
When you create a nickname for a data source object, metadata about the object is added to the global catalog. The query optimizer uses this metadata, as well as information in the wrapper, to facilitate access to the data source object. For example, if a nickname is for a table that has an index, the global catalog contains information about the index, and the wrapper contains the mappings between the data types and the data source data types.
Nicknames for objects that use label-based access control (LBAC) are not cached. Therefore, data in the object remains secure. For example, if you use the Oracle (Net8) wrapper to create a nickname on a table that uses Oracle Label Security, the table is automatically identified as secure. The resulting nickname data cannot be cached. As a result, materialized query tables cannot be created on it. Using LBAC ensures that the information is viewed only by users who have the appropriate security privileges. For nicknames that were created before LBAC was supported, you must use the ALTER NICKNAME statement to disallow caching. LBAC is supported by both the DRDA (for data sources that use Db2® version 9.1 and later) and the Net8 wrapper.