If your database contains opaque data types, distinct data types, or named row types, you might want to create user-defined casts that allow you to convert between the different data types. When you want to perform conversions between two data types that have the same storage structure, you can use the CREATE CAST statement without a cast function. However, in some cases you must create a cast function that you then register as a cast. You need to create a cast function under the following conditions:
The following sections show how to create and use user-defined casts that require cast functions.
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