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Add support for a new kind of function which will return anonymous tuples i.e. a table.
These functions will have to additionally specify a return type resolver that returns an anonymous tuple, which may optionally allow "ordinality".
The ordinality is something that serves as element index and is common on many databases.

It would be cool if we could add a few standard table functions like

• unnest - unnest arrays to rows

• generate_series - generate a series of values => See

• split - split a string to rows => See

Note that this is going to be an incubating API, since users will be able to implement custom table valued functions.