Implicit casts
The database server automatically resolves internal function signatures
for a subtype that inherits a function from a supertype in the following
two cases:
- Distinct types
- The database server automatically creates casts between the distinct type and source type.
- Opaque types
- You must create the casts to support a type hierarchy.
You must first create a cast with the CREATE IMPLICIT CAST statement for it to be used implicitly during the execution of a query. The query optimizer tries to find implicit casts when it tries to make arguments fit support and strategy function signatures.