Add within group clause support for aggregate function builder

[ivashog]

closes #781

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Name	Status	Preview	Comments	Updated (UTC)
kysely	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jul 22, 2024 11:20pm

[ivashog]

@igalklebanov, I want to consult about the API of the future within group () functionality.
I see the following possible varaints:

1. Extended - fn.agg('mode').withinGroup(wg => wg.orderBy('field')):
   + : looks like SQL
   - : too verbose; need to create separate WithingGroupBuilder
2. Simplified - fn.agg('mode').withinGroup('field'), because within group () use only order by expression
3. Also I can try to implement both variants in one method

[igalklebanov]

@igalklebanov, I want to consult about the API of the future within group () functionality. I see the following possible varaints:

1. Extended - fn.agg('mode').withinGroup(wg => wg.orderBy('field')):
   + : looks like SQL
   - : too verbose; need to create separate WithingGroupBuilder
2. Simplified - fn.agg('mode').withinGroup('field'), because within group () use only order by expression
3. Also I can try to implement both variants in one method

Hey 👋

We had a similar situation with filter (where ...). All current SQL specs only support where clause there, so we decided, for simplicity, to just go with filterWhere(...).

So I'd go with withinGroupOrderBy(...) for now. WDYT?

[ivashog]

Hey 👋

We had a similar situation with filter (where ...). All current SQL specs only support where clause there, so we decided, for simplicity, to just go with filterWhere(...).

So I'd go with withinGroupOrderBy(...) for now. WDYT?

OK! We think in the same direction)

c81d766#diff-0e4fd806a08c99c93c0331a3d0e75d4c726e4face483d2e21a9febe03e944593R167