Support additional aggregate functions

[justinj]

• [ ] bool_or
• [ ] bool_and
• [x] array_agg

Probably more! Please comment on this issue if you encounter others we're missing.

See here. These are aggregates that return the OR/AND of their inputs. Note that their behaviour is actually distinct from the dataflow Any and All aggregates in the presence of NULL.

[justinj]

Going to generalize this to missing aggregates more broadly.

[frankmcsherry]

Note that their behaviour is actually distinct from the dataflow Any and All aggregates in the presence of NULL.

But they can be determined from dataflow Any and All, right, by mapping NULL to true and false, respectively?

Ah no they can't because while they ignore NULL in their inputs, they produce NULL on empty inputs. What a world!

[frankmcsherry]

We should probably just delete Any and All and require everyone to rewrite aggregates in to Sum and finish with the domain-specific logic they require.

[wangandi]

Related: #2813

[andrioni]

It would be nice to have list_agg here, as it could provide (I imagine) a more efficient alternative to jsonb_agg in several cases.

To be clear, I would prefer for list_agg to return a proper list, similar to array_agg, instead of the SQL2016 version that returns a string.

[benesch]

@andrioni just a heads up that list_agg and array_agg just landed!