Creating a cast that has a cast function
About this task
You can create special SQL-invoked functions, called cast functions, that implement data conversion between two dissimilar data types. When two data types have different storage structures, you must create a cast function that defines how to convert the data in the source data type to data of the target data type.
To create a cast that has a cast function:
Procedure
- Write the cast function.
The cast function takes the source data type as its argument and returns the target data type.
- Register the cast function with the CREATE FUNCTION statement.
- Register the cast with the CREATE CAST statement.
Use the WITH clause of the CREATE CAST statement to specify the cast function. To invoke a cast function, the function must reside in the current database. However, the cast function does not need to exist when you register the cast.