The “from-sql routine” and the “to-sql routine” create a mapping between a UDT and a pre-defined type. This pre-defined type is called the external type of a UDT. A client application only deals with the external type; it does not deal with UDT value directly.
External Type Example
For example, if the following conditions exist:
Then, during an retrieve of FULLNAME values, the Teradata Database server converts the values from FULLNAME values to VARCHAR(46) values by invoking the “from-sql routine” associated with the FULLNAME UDT.
Note: The client must expect to receive the data in the same format as it receives VARCHAR(46) values.
Similarly, when values are provided by the client for insert into a FULLNAME UDT, the client must provide values in the same way it would provide values for a VARCHAR(46) field. The Teradata Database server will convert the values from VARCHAR(46) to FULLNAME values using the “to-sql routine” associated with the FULLNAME UDT.