Do all rows from a set have the same TupleDesc?

[Raúl Marín Rodríguez]

Hi,

I have an user defined aggregate (Postgis' St_AsMVT) that receives rows as
input and I was wondering if all these tuples have the same TupleDesc.

In case it's important, here is how it's normally called:
```
SELECT St_AsMVT(q) FROM (
SELECT * FROM tilertest.tract9double
) q;
```

The idea behind this question is that, if this were true, I could cache
some information (number of attributes, oids, some internal stuff related
to each attribute) until the end of the aggregation to avoid having to
retrieve or calculate them for each one of the rows.

All the tests I've made seem to confirm this is true, but I was wondering
if
there is any guarantee.

Regards

-- 

*Raúl Marín Rodríguez *carto.com