Jeff Janes <jeff.janes@gmail.com> writes: > The docs for creating aggregates for 9.6 and beyond say: > "For aggregate functions whose state_data_type is internal, the combinefunc > must not be strict. In this case the combinefunc must ensure that null > states are handled correctly and that the state being returned is properly > stored in the aggregate memory context."
> Since combinefunc with an internal type is only useful when serialfunc and > deserialfunc are also defined, why can't the built-in machinery just do the > right thing when faced with a strict combinefunc?
The issue is how to initialize the state value to begin with.
Why does it need to be initialized? initializing a NULL state upon first use is already the job of sfunc. Can't it just be left NULL if both inputs are NULL? (and use serialize/deserialize to change the memory context of the not-NULL argument if one is NULL and one is not NULL)