On Fri, Jun 9, 2017 at 9:06 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Jeff Janes <jeff.ja...@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) Cheers, Jeff
