Fix aggregate function on litteral

[VincentLanglet]

Closes #460

Since you introduced this in #232, I'll be happy to have your review @arnaud-lb

When doing a SUM, I think the type must be "ungeneralize" (cf #460 )

When doing a AVG,

• if the value is not constant, I think the type must be "ungeneralize" too
• also, I got a failure without $type = TypeCombinator::union($type, $type->toFloat(), $type->toFloat()->toString()); because the AVG value computed in my tests was 1.0 or '1.0' (even for AVG(1)) and not 1or'1'` so I think we need to add the float result (and the stringified float result).

[VincentLanglet]

Seems like

$type->toFloat()->toString()

doesn't do what I was looking for @ondrejmirtes, I may require your help to end this PR.

If I have a ConstantInteger(1), I can get a ConstantFloat(1.0) with the toFloat method.
What would be the recommended way to get a ConstantString('1.0') from this float now ?
The toString method is giving me a ConstantString('1')...

[janedbal]

I'm using generalize for those cases (expand QueryResultTypeWalker)

[VincentLanglet]

I'm using generalize for those cases (expand QueryResultTypeWalker)

I used generalize for the SUM method.

But if we're doing AVG(1) if thought this was better to return 1|'1'|... rather than float|int|numeric-string|null but after a good night, I think it's maybe a useless edge case to handle.

[janedbal]

For AVG, it is edgecase, but the same issue for SUM is not.

[arnaud-lb]

LGTM!

[ondrejmirtes]

Thank you.

[VincentLanglet]

Your welcome

Since 1.3.x is not the base branch it didn't closed automatically the issue #460 @ondrejmirtes