The source data type from the cast definition.
Either source_data_type or target_data_type or both must be a UDT.
Example: Dropping the Cast of a Geospatial UDT to a Geospatial UDT
The following example drops the cast of UDT circle to UDT ellipse.
DROP CAST (circle AS ellipse);
Example: Dropping the Cast of a Geospatial UDT to a VARCHAR
The following example drops the cast of UDT circle to VARCHAR(32).
DROP CAST (circle AS VARCHAR(32));