docs: Add docs for Relation literals

[max-sixty]

I've combined it with the from_text page, as I think they're similar (and I put these first since I think they're generally better).

One question — do we want any keyword for them — e.g. from_lit {...}? I don't think we necessarily do, but wanted to raise it, since it's the only construction which can be directly in line now.

[aljazerzen]

If you want, you can use:

from {[a = 3]}
select a

... because from is already just a noop function. Its only utility is "pulling from database tables" instead of normal name resolution.

I'd say let's not add too much unnecessary functions here.

[max-sixty]

If you want, you can use:

from {[a = 3]}
select a

... because from is already just a noop function. Its only utility is "pulling from database tables" instead of normal name resolution.

I'm going back & forth on this!

• from seems incongruent applied to arrays — they're not table names — and from brings tables into the query.
• But having it bare also seems out-of-place, (image below) — there's no transform bringing the array into the query....
• But then we introduce another transform from_lit?!

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FWIW having from was a question we went back & forth on in the very early days of PRQL — I originally just had artists. I think we were correct to make the change — queries look more cohesive with from artists than just artists.

Any thoughts from others?

Otherwise I guess we go with the existing state and see how we feel... I don't have much beyond aesthetics here, so we shouldn't wait at all.

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FWIW let makes it look more reasonable (but we obv can't have different semantics inside & outside a declaration)

[eitsupi]

My preference is starting with from. (The word "lit" does not seem very clear to me.)

Given things like from foo.csv and from df (df is pandas.DataFame on Python) in DuckDB, I wouldn't mind putting something other than table name after from.

[max-sixty]

My preference is starting with from. (The word "lit" does not seem very clear to me.)

Given things like from foo.csv and from df (df is pandas.DataFame on Python) in DuckDB, I wouldn't mind putting something other than table name after from.

This resonates with me...

[max-sixty]

Merging this; with a note on us considering from...