Now that all aggregate functions are derived from
stateless_aggregate_function_adapter, we can just fold its functionality
into the base class. This exposes stateless_aggregate_function to
all users of aggregate_function, so they can begin to benefit from
the transformation, though this patch doesn't touch those users.
The aggregate_function base class is partiallly devirtualized since
there is just a single implementation now.
We will want to reuse the functions that we get from an aggregate
without making a deep copy, and it's only possible if we get
pointers from the aggregate instead of actual values.
Makes final function and initial condition to be optional while
creating UDA. No final function means UDA returns final state
and defeult initial condition is `null`.
Fixes: #10324
Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
A user-defined aggregate is represented as an aggregate
which calls its state function on each input row
and then finalizes its execution by calling its final function
on the final state, after all rows were already processed.
